bigwei is right on with the carfax and http://kbb.com.
I think what you’re really asking is how you find a mechanic to check out the vehicle. If you have a mechanic, just use him and have the person meet you at the mechanic’s place to check it out.
If you don’t have a mechanic, I would get on the phone and call around to the shops closest to you. Ask them what they would charge to look at a car you’re thinking of buying. They’ve dealt with this before so it’s no problem. There might be a charge, there might not. Just be prepared to pay something for having them check it out.
I’ve bought a couple of cars like this. It is extremely important to make sure a mechanic sees the car. Once, There was $700 worth of repairs that needed to be done on a car I was buying. The previous owner paid the bill to get me to buy the car. Good stuff. I would have been pissed if I had found stuff wrong with the car after the purchase.