Any cracks or scratches on it.

You should look for personality. Good acoustic guitars can be found everywhere. They dont have to be name brand for them to be good. Just make sure that the neck isnt wharped, bridge isnt loose, and the tuning keys still turn effectively. A good one to learn on is a classical guitar because the nylon strings are easy to hold down and they also have wider necks forcing you to stretch your fingers. Steel strings are louder and much more crisp, but the strings dont last as long as nylon, but they are easier to tune and stretch.

If you want a very good acoustic, it's not exactly an acoustic, but it is a hollow bodied guitar, called a Jazz Guitar. they have "F"-like holes in them and they prodouce a rich, clean tone.

1. Sound - as with a new guitar, make sure you like the sound. Play guitars in the music store and find a sound you like. Think about why you like the sound of this guitar better than others. Then find a used one with a similar sound. 2. Tuning - when the open strings are tuned, does the guitar play in tune all the way up the neck? Do the harmonics at the 12th fret match the fretted notes at the 12th fret? This is called intonation. On some electrics, it's almost trivial to fix this problem. On acoustics it's not - if there is a tuning problem, pass on it and find a better one. Bring a tuner with you if you need it, but only reject based on intonation if you can't live with the sound, or it is out by tuner by more than about 5 cents. 3 - Machine Heads - do they operate smoothly (listen to the pitch of the string as well as feel how it turns), are they really difficult to turn. On even the best guitars, you should always tune up, rather than down, to pitch. Do this, give the string a little tug, and tune up again. This is the tuning method I use. Is it easy to tune the guitar you are looking at like this, or does the pitch change in a way that means you can't tune it? If so, find another. 4. Condition. Are there any obvious signs that the guitar has been abused or not looked after? Are there cracks, splits, or extensive peeling off of lacquer? Do the frets protrude from the edge of the fretboard, even a little (if so, the wood has dried out, also you might cut yourself on the fret ends). If any of these, find another. If the guitar is being sold in its original case, this is good, as it will probably have lived in it. 5. Action - The action refers to the string height, and how easy it is to fret notes and chords on the neck. People like different heights. Make sure you can play the music you like on it without hurting your fingers. If you don't play, bring along someone who does. Actually, if you don't play, they should do all these checks. 6. Electrics - if it has a built in pickup, check that it works, and sounds OK (ideally through an acoustic amp or PA, but a guitar amp will do). Take a look inside the battery compartment if present. Operate all controls (EQ etc) and make sure they work. Jiggle the jack around at the input and check for crackling noises. 7. Ask questions. Why are they selling it, how long have they had it, has it been gigged, how long have they been playing guitar, are they in a band, what sort of music do they like. Chit chat. This might just confirm or raise suspicions to you about it. If you are not experienced with guitars, take your time and don't rush it to pretend that you know what you are talking about. Best of luck