Nice Vintage Markets

I’m going to check out the Nice, France vintage markets on Monday and I was wondering if anyone has tips for buying at these. I’ve always wanted to pickup a completely random, watch at a flea market but when it comes to used vintage, I’m not sure what to inspect before purchasing. Like is there specific type of dial patina/wear that comes from moisture as opposed to sun exposure? Stuff like that. Thanks in advance to anyone that responds and I totally realize this might be a non-specific type of request.