Regarding used guns in general- don't let that worry you. Very very few guns on the used rack have that many rounds through them.
Here's what I usually look for
-Obvious ham handed modification attempts like bad attempts at stippling, bad refinishing, obvious tool marks, and so on. Not super common, but pass anyway.
-Uneven wear on frame rails, locking blocks, breech face, and other internal parts. However, most used guns will have almost no obvious wear at all.
-Cracking on the frames or breech face.
Happily, you'll find that most used guns have hardly been used at all. Once you get it home, it's a good thing to research what the regular replacement intervals are for parts and springs, then just go ahead and replace them right away. Springs, pins, and locking blocks (Beretta 92) are fairly cheap and easy to swap out.