The guitar is made by a living material, wood, and just like any living material, no two guitars are alike. The Australian physicist Joe Wolfe : "Wood is not a predictable material." (I guess you do not have to be a physicist to figure that out!). This is in part responsible for the often heard relation between the guitar unpredictability and woman's unpredictability... I personally think that men and women can be equally predictable or unpredictable according to how you want to see it.

The motion of the strings acts like a pendulum and each string creates a very complex and unique pattern. Then, to add more complexity, each note creates its own very unique pattern within the pattern. Whenever an E, F or G are played on the 6th string, the guitar inflates like a balloon. The top and back of the guitar move closer and away from each other in terms of microns per second. The higher the notes and the strings we pluck, different parts of the sound board and back vibrate.  The braces underneath the sound board, divide it so as to allow for different parts of the board to vibrate according to the string plucked.

The above image, although hyper simplified, shows a very straight forward fact: The guitar is a simple instruments to build. A few parts of construction like shaping of the neck and head, thinning of the top and routing for bindings require talent, practice and concentration. Still, anyone pretending that he is a rocket scientist for building a guitar, is lying.

Every luthier has a plan with all the measure of every single piece of wood. Plans can be bought and it is just a matter of deciding which model to build. What you will find out eventually is that they are all, practically speaking, identical. They are all based on the Torres model. Some have an extra strut, or a strut less. Still, others make the struts longer or shorter... no matter what they do, the variation is unperceivable to the human ear. Just remember that a Stradivarius can barely be told apart from other violins even by experts, let alone a 2000 dollars guitar. 
Guitar builders need the basic tools of a carpenter. All the parts, except for the neck, are straight, so, no special sculpting tool or skill is needed either. Bending the wood is as easy as heat and pushing. Below is a bending iron.... 

The sound board is the most important source of sound on a guitar. Spruce,  redwood cedar and pine (Canadian, Spanish, Italian) are the favorite top selections for this key part of the guitar. Builders look for trees that have grown slowly, usually found on cold mountains. The reason is that the density of the wood and the wood fibers will be higher. Pines are usually the trees that grow at higher elevations. The builder can tell about the density of the wood by hitting it gently with his knuckles. Specialized wood sellers do the selection for you.

Luthiers can only make a few dozens guitars each year and this allows for little scientific experimenting. This will always make luthery remain more of a craft than a science.
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Few guitarists need to spend more than 1,000 $ to play  at their best and,  playing well, is seldom associated with the price tag on the instrument. I often play on my old 100 bucks instruments. (I keep my old instruments). The ones built in the 70s (mine), focused on playability (good approach) Sound was poor at best but that was why you dreamed of owning a concert babe.... After the 80s, with the advent of Yamahas and Takamines and all sorts of factory guitars, a whole new breed of laminated instruments invaded the market. These impress the ear but are impossible to play and induce the player into acquiring every possible left hand technique defect available. If you are  a beginner today, you MUST buy a cheap concert guitar so you will play THE RIGHT WAY from the beginning. Avoid being one of the millions who fall in the 400 bucks Japanese guitar  trap only to end up frustrated for not going anywhere with your sound and  playing. The cheaper the guitar, the harder it is to play (to achieve a given musical/technical result)
   Guitars in the 7,000-15,000+ US$ price range are rip-off instruments. The incredibly high cost of living in the US, Europe and Japan partially explains some insane prices...The truth really lies in the fact that since most luthiers only build a few instruments a month, they have to "make all their living" selling 2-3 instruments a month. Free markets can easily become circus market. As a rule of thumb, remember that if a luthier were to buy the rarest woods and the most expensive tuners and accessories, he would not spend over 1,200 US$. Naturally, astronomical figures can also be spent on some ridiculous accessories as the tuners. Some brands cost well above 1,000 US$. A 300 $ tuner will last 2 lifetimes, spending more than that is also crazy. Changing 40 bucks tuners every few years is, in my opinion, the best option. The real case scenario is that materials add up to approximately 400-600 US$. There is no reason why some guitars can cost so much. It doesn't matter what the seller says. A few extra bindings and some exotic woods can only add up a few hundred dollars.... The key element is a talented builder, one who has a natural intuition with wood and can create a musical instrument.

FACT: The more you spend on a guitar, the better you will be expected to play LOL! 

Wood selection is perhaps the most important part of the building process. It is known today that the wood used by Stradivarius for his violins built in the 1700-1720 span of time were built using woods that grew in what scientists call a micro ice age that hit Europe from the mid-1400s until the mid-1800s...making trees grow much slower than normal. "Grissino-Mayer at Tennessee and Dr. Lloyd Burckle at Columbia suggest a "Little Ice Age" that gripped Europe from the mid-1400s until the mid-1800s slowed tree growth and yielded uncommonly dense Alpine spruce for Antonio Stradivari and other famous 17th century Italian violin makers". It is essential that you trust your builder and those that provide him with wood. 

The above chapters have sent a wave through the bones of many builders and guitar dealers the world over. I have been the target of all types of defamatory comments in different online media. My students deserve to know the truth and I sincerely could not care less. Hundreds of players enjoy my instruments and saved themselves from spending astronomical sums of money for NOTHING ! The facts speak for themselves. 

Becoming obsessed with the looks of a particular cut will most likely make you overlook more important factors like exceptional density, grain flow and mineral streak.

(This formula only applies to new instruments... antique or collection instruments are valued differently).  Antique guitars sound sloppy. They were not built like Stradivarius violins...they were the first attempts by amateur builders... so, if you buy them, prepare yourself for the disappointment of your life. Some nuts out there offer these for over 20 or 30 thousand US$...simply crazy...and some people are even crazier to buy them !! I only cherish instruments that were played by great guitarists because they were a part of the artist and instruments that were highly decorated because those are true masterpieces. Unrepeatable. Check Barrios Mangoré guitar from the 1800 Surviving Barrios Mangoré guitar

Agustin Barrios' guitar

The lure that traps many guitarists to buy these expensive instruments is that the player thinks that playing on the expensive guitars is easier. FALSE ! Spanish instruments in particular are difficult action instruments. The Spanish luthier school grew around Segovia and I am sure you have seen Segovia's hands...huge and fat...this translated in muscular mass which made it easy for him to play these instruments. This is not the case with most players. Especially the non professional players. 

You do not buy an F1 Ferrari to go around the streets of your town but a production Testarossa.

Today, guitarists have  many choices of splendid instruments available. I will  share with you what  I would do if I wanted to buy a guitar today. There are a few things you have to keep in mind:  Where will I play my guitar most of the time? Will it be a concert hall, a club, a recording studio? Will I use a microphone and a PA? (In the black and white picture, Segovia is looking at my guitar in his studio)

In the 80s (the decade of extremes),  guitar constructors and players were trying to create instruments to play as loud as possible and show the world that the guitar was a "real classical" instrument (as if "classical" and "loud" were synonyms). Some of these instruments were literally wild beasts that had to be "tamed" more than played. With all that, I have attended concerts where these instruments were played and you could barely hear them if a mosquito flew passed too near and you did not have the cash to sit in the first 10 rows. So, eventually, with the advances in electronics etc., you would see the concert players using microphones and pickups to amplify their instruments. Luthiers, on the other hand,  realized that they were putting the hard work and the money in the wrong place. The worst part about it is that for every decibel in volume projected, you had to invest 3 or 4 thousand dollars and you could only increase the volume "so much".  Sound quality depends on the plucking technique used and, the rest, is suggestion or illusion. For the past 2 decades or so, guitar constructors have been focusing more on making the playing experience more pleasurable and solving the real problems associated with guitar performance, is slowly becoming the main goal.
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What are the features you should be looking for in a guitar? I think that the best way to go about it is the following:

-Do not ask too much information about brand, wood, etc.  The heavier the instrument, the better. It will stay in place better and you will be able to build a solid technique around it. In any case, when you order a concert guitar, specify if you like heavy or light construction. 

-Buy new musical instruments.

-With Spanish guitars watch out for the following TRAP: Spain is one of the driest countries in Europe, especially Madrid. If the place where you live is not as dry, allow for some time of adaptation for the wood. More dangerous than the dry-moist guitar trips are the moist-dry ones. The wood will tend to lose humidity faster than the wood allows and you can see cracks appearing all over the varnish, wood and even the fret board (the frets will stick out either at the top or bottom (or even both) of the fret board. The immediate thing to do in this case, besides crying, is to put your guitar in a bathroom and leave the hot water on for a few hours. 

-If you are new at the guitar, then it is likely that you are not sure of what to look for and how a guitar should feel in your hands. If that is the case, allow the builder or your teacher(s) to help you choose wisely. 

-If money is a deciding factor, wait. It will not be long before you can afford a more "unique" guitar. 

-Keep an open mind when it comes to choosing your guitar.  I have witnessed the following anecdote in 1986:

  John Williams (the guitarist) was about to give a concert for BBC in downtown London. It was a noon concert with live FM broadcast. Williams was going to play his Fleta. An "unknown" luthier approached him  with a guitar in his hand and said in an Australian accent: 

-"Maestro Williams, I build guitars. I would like you to try mine". 
Williams reached out to grab the guitar and, while standing, played a couple of fast arpeggios on the guitar and said...
-"Good. I will play it right now!"

Williams got on stage and played the concert with the Smallman guitar. He still plays Smallman to this day.

I have since heard and seen Williams play with this guitar in all kinds of halls, all kinds of repertoire both amplified and non-amplified. What it teaches is that from a player's point of view, all that really matters is how the guitar sounds and if it captures your imagination... the rest is nonsense

I say this because since I decided to sell the Paraguayan guitars on my website, I receive the most incredible questions by some novice players which show that, very likely, they will end up playing the guitar everybody else says is the right one.