Go to a reputible place, such as an Esso Car Clinic or a business that's been around for years.
You should be able to tell if a place will give you the service you want by:
1- They should charge you at minimum 1 to 1 1/2 hours of work.
2- They should give you a detailed written report, and this should include:
-compression of all cylinders
-condition of brake system, struts, springs, exhaust system
-general body shell condition
3- They also should take the car for a short drive.
I have bought 4 cars and gone through these pre-purchace checks at different places and I believe I got what I paid for.
Remember, if the mechanic did find something wrong you don't have to pay to get it fixed. Simply return the car to its owner and move on to your next interested car.
1996 E36 M44 318i 5sp LSD