Bows have horrible resale I would say if the bow is 2 years old. I would only offer about 250 or 300 for it and thats pretty generous also based on the fact that who ever is selling it may have shot the piss out of it and just telling you it was hardly shot just to get the sale. I would try to get him to come down on the price and before you buy it make him give you a guarentee that there is nothing wrong with it and that you can bring it back if there is something wrong with it for a return or repair at no cost to you for a period of atleast 30 days.
Also see if you can shoot it first to make sure everything is working properly. Is it at a archery shop or is it a individual selling it?? If it is an individual selling it see if he would mind taking it to a archery pro shop in your area to get a overall inspection to make sure it is sound.