While I would usually agree with larry's advice, here's an example of a situation that isn't just black and white.
If you have two vehicles, and we assume that both have been maintained exactly, and all service records indicate proper service intervals, the price for each one is very close, but their mileage on the odometer is say, 30,000 or even 15,000 miles apart, would you rather:
1. Buy the lower mileage car that is approaching a major service interval that can be somewhat costly?
2. Buy the higher mileage car that has already passed that major service interval, and just had the work done?
When I bought my Aerostar, it was at 56,000 miles. Just 4,000 miles short of the factory required 60,000 mile service. If I hadn't been aware of that service being required, and hadn't negotiated for the service to be included as part of the sales agreement from the dealer, I would have had to spend an additional $700 for the 60K service about four months after the purchase...
Buy the car based upon service records, proper maintenance, condition, and what work will be required after the purchase.
Here's some could be expensive points to consider:
When was the timing chain last replaced?
When were the valves last adjusted?
What condition are the brakes and tires in?
Does the climate control system function properly?
What oil leaks are there? How are those oil cooler lines?
How are the motor mounts?
How's the transmission? When was it last serviced?
Do all of the power accessories work?
How's the paint and interior?
And finally, how does the asking price compare to what the actual NADA and Blue Book values are?
http://www.kellybluebook.com/
http://www.nada.com/