TOPIC: Used Guitars

I have a question for some of you who are more experienced than i. Sometimes good deals can be found on used acoustic instruments. I'm talking garage sales, flea markets and such, and not real high end instruments, although one could get lucky there as well. Aside from obvious physical abuse to the body, what should be checked aside from obvious physical damage that can be seen (warped or bent neck, loose machine heads, cracks, bridge and headstock damage)If it checks out visually, what can be hidden? I've heard cracks are a death sentence for acoustic guitars, and can be hidden. If it tunes up ok, is there a way to fret a note on a specific part of the fretboard to check the intonation quality? After tuning it, if the 12th fret notes show the correct octaves of the open strings with no buzz, is this a good test? I just don't want to miss something on an apparently good deal, but don't want to inherit an abused instrument...alas, the paradox of buying anything used!

If I was looking at used instruments, I'd make sure I had my tuner with me (it could save your life someday) and just noodle with it for awhile and see if it stays in tune.

Yes indeed! A tuner, a pick, and a good eye.

I thought it was a capo that could save your life some day???
But I guess you would need that (working) (used) guitar first!?

There's many things that you should look for. Of course the physical shape of the guitar (shape=condition) needs to be addressed. Wear and tear doesn't automatically mean the guitar is bad. Some folks play harder than others. Mojo can be a good thing.
Look down the neck to see it's condition. There should be a slight bow in it, away from the strings and back, from the headstock to the body. Not a lot, but enought so you can see it. The action should render the instrument at least playable. Just play it to feel that. You can tap the top at different places to try to detect any loose braces. Look at the nut and the bridge. If the bridge is almost nil and the action is very low, the guitar may be a candidate for a neck reset soon.
Cracks don't always mean the guitar is no good. One of my favorite guitars has 4 body cracks and still plays wonderful. The cracks should not be gaping and still match up well. If this is the case, it can be repaired correctly and still be stable. If you see a crack, try to see it from the inside and see if there arew any cleats holding it together. They usually look like small, bowtie shaped wooden pieces across the crack.
Look for any shadows around the bridge, the pickguard or any seams where they shouldn't be. If bridge repalcement isn't done by somebody who knows what they're doing, the intonation might be way off due to the wrong placement. Look for obvious signs of work.
This is, of course, only a small example of what to look for. I'm sure this list can be added to a lot. Also, a lot of things can be fixed but will cost money to do so correctly. You have to weigh the worth of the guitar to the repairs needed to how much you like it.

Eye ball down the neck, like your sighting a gun. If there is not a truss bar adjustment, your sunk. I always advocate buying a quality guitar, not that you have alot of choices at a garage sale, but you never know. A vintage 63 strat was found in the back of a closet at a yard sale, I won't mention any names here though.