Well I am no expert but I can tell you what to look for from experience of buying 3 myself.
Do not trust anyone's opinions about the machine. See if for yourself in person because one person's idea of something being in really good shape my not be the same as yours. I don't care if it is someone who owns 100 pins or even someone who restores them for a living, see it for yourself... Bottom Line.
Check for playfield wear because the pf is one of the hardest things to replace. Also look for sloppy touch ups on the pf. Check to see how the game was treated, is there a lot of built up dirt on the pf or has it been shopped lately. If it needs shopped, think about if you are up to the task of doing so.
Check for DMD out gassing or dot credits. You can do this by running a test in the service mode of the machine.
Check for switch errors. Play the machine a few times and then turn it off and back on, watch for switch errors.
Look at every side of the cabinet, inside and out including under the pf.
Here is a link to the service manual:
http://www.ipdb.org/files/2852/Williams_1995_No_Fear_Dangerous_Sports_English_Manual.pdfDownload it and look it over before you go to see the machine so you know a little but out the test modes.
Good Luck!