Location might definitely affect price, so I cant really tell you what to expect as far as that goes. But I wouldn't expect to see all that much of a difference as far as values go. I would recommend going online to various sites, and comparing values. I'd also go to a book store and check out used car guides, because there may be a difference from what you see online and in those books. What will affect the price of a car is the condition its in. So you should be cautious of a deal that seems too good to be true.

Thats why I recommend having a good look at the car. Definitely get the VIN numbers on the cars you look at and run them through carfax. This doesnt guarantee that there wont be problems that werent reported, but its an excellent resource nonetheless.

Take a good look around the engine. Make sure there arent oil leaks and check the condition of hoses and stuff. If you can get them to start the engine when cold that would be good, you can see if it has problems starting. Once the car is started let it warm up and check to see if it has a smooth idle.

As for checking compression, its possible you could get the dealer to check for you. I recommend being there and watching him do it so they dont try to pull one over you.

You could do it yourself, but you'd have to buy the guage for it. I dont think its too expensive. If you look around on old forums here you can probably find out what the compression should be; I cant remember right now the exact range is.

What you really have to look for is that the compression for each cylinder is the same. You can have a difference of up to 10psi and still be within acceptable tolerances. But ideally, there should be almost no difference.

But look for other signs of wear. Look carefully for indications that the car may have been in an accident, body panels not fitting right, inconsistencies in the paint, stuff that doesnt look like its in the right place, etc.

Another thing to look at is wear on the seats and pedals. Highway mileage is always better than city mileage. If the pedals and seat show more wear than another car with roughly the same mileage than its a good bet the car was driven off the highway the majority of the time. This means more wear on the transmission and engine. Also remember to check for odd noises if you test drive the car. Not necessarily coming from the engine, but from the wheels and suspension.

I hope this is helpful. Its a lot, but I was trying to cover everything I could think of. I'm sure there are people here who could give you additional, and more detailed information on what to look for.