I've had 3 of these chaps in the 18 months I've had a darkroom so, based on that and my own reading (kept upgrading to more featured models, nothing actually wrong with any of them - I think I'll stick with my latest AC1200 version for now...)
As with all things, condition & age is everything but in general the L1200 is one of the best there is. Intended for professional labs it is solidly made. As with most enlargers, there is little to go wrong. The head (sprung) should move smoothly up and down and lock solidly.
Make sure you have all the parts as new replacements are usually available but very expensive. You will need negative masks for all formats you are likely to use and the appropriate mixing boxes (if a colour head) - you can get by with using a 4x5 mixing box for everything but it makes exposure times longer. The older bellows can be a bit brittle and go at the corners but this is more a bargaining point than a serious problem...
Which head does yours have and which lenses? This will effect the fairness of the price asked. If a CLS450 or more recent colour head and decent lenses (it's likely that they are as this is normally a Pro enlarger) then it looks a very good price if I convert Dollars to Pounds Sterling, but I'm not sure what they normally go for in the US.
Bob.