If it is stock, hook a vacuum guage to it and make sure it pulls 20 in. hg. at idle. That is a sign of good general engine health. Look at the oil and coolant, do they look clean. Same with the tranny fluid. Crawl under it and look for rust and body damage, not to mention leaks. Dont forget to drive it, at least up to 70mph, if it shakes real bad up there this is the only way you will know.