First of all, welcome to LTG.
Secondly, we have a search function here (you can see it next to FAQ, members, control panel in the upper right corner of the page). Just his the search button, type in F112 into the search box, hit send and you'll see 2 or 3 years worth of entries about F112 guitars.
Thirdly, they are great guitars. They are Guild's smallest 12 string model and the sound comes out bright and quick. F112s are a great place to start appreciating the large and varied family of Guild 12 strings. The bigger models (f212, f212XL, etc.) have more of a baritone sonority to them (they are louder but 'slower'), but they are all good. I think 112s work well in lots of different applications; ensemble playing, duo or solo playing, almost anything. Lots of wonderful jangle, although I don't know that the bigger 12s might not project farther into the performance room that you will be playing in, etc.
Things to watch out for when you are buying are cracks in the top (and, be sure to look on the sides of the fingerboard for cracks that run along there), soundhole waffling or rippling, bridge lifting, one or even two cracks in the back of the neck, underneath the 3rd through 7th fret area (it means that one or both of the dual truss rods in the neck was tightened too much and cracked the back of the neck; not good!) and the need for a neck reset. Oh, I can't remember how bad '73 tuners suck, so that can be another potential problem.
Don't pay too much, because you don't know what it will cost to repair, blah blah. If they'll let you take it to a luthier for an evaluation, so much the better. Take pictures and post them here, especially of any problem areas. That way, we can help you figure out what you have and what the guitar needs to be in good shape.
When I say pics, you don't have to have a $1000 digital camera, but it helps if they're not just cell phone pics, too (something I am frequently guilty of, by the way). If you don't know how to post pics on web sites, we can talk you through that, too.
Have fun!!