First let me say this as I do not think I can stress it enough. If you are buying a Used Car, I do not care if it is from a dealership, an individual or a friend you always run a CARFAX history report to make sure the title is clean and there has been no major reported problems. The other thing you always do is have the car inspected by a mechanic. If your buying at a dealership take it to a different mechanic! This applies even if the used car comes with a warranty. If you do not do this than you are the only one to blame if there are problems!
A Few Common Terms for Used Car Buying and Selling
Private Party Seller- An individual selling a car not a dealer.
Retails Sales Price/Value- The price the car should be listed at from a dealer.
Private Party Sale Price- The price the car should be listed at (asking price) from an individual.
Trade-In Value- The amount that could be expected for the car if traded at a dealership.
As Is- This means the car was sold "as is" and there is no warranty. If it breaks in half as you drive it off the lot, well you own both halves.
There is no set price that a dealer pays for a used car. So it is impossible unless you have an inside connection at the dealership to know what the dealer has paid for it. The best thing you can do is some good old fashioned research to try and make an educated guess as to what he may have bought it for. Better yet do the research and figure out what number you can buy the car for and still get a good deal. (skip to 8 steps for buying a used car and saving money.)