I've used armslist. Depending on where you are probably will determine your experience. I'm in indiana so I wasn't worried about much. The best advice I can give if you are going to go make a deal is make sure you come "prepared" in case the deal goes sour. There is a lot of money on the line usually and deals don't necessarily happen in the most inviting of places.
Thanks gentlemen, I'm looking for sales on the up and up, probably deal with the dealers mostly but thanks for the input. I've had nothing but good experiences from craigslist so things should be fairly the same.