If someone HAS to ask for this advise I would give advice similar to purchasing any Chameleon from anywhere for a beginner, if you know what you are doing all the below is null and void. My check list in order of importance below:
Step 1: Confirm Captive bred and born. If answer is "Long Term Captive is the same" or "I'm not sure" or "No" pass, it isn't worth it.
Step 2: Check all the places that the skin opens for anything weird. Eyes, nose, mouth, nails, and the rear venting. Eyes should be clean, clear and alert, mouth should be clean and aligned properly, nose should be clean, nails should all be intact and everything in the back should be clean. No exceptions, no excuses, not worth the risks.
Step 3: Skin should clear of stuck sheds, parasites, or any weird bumps. Anything other than a vibrant looking skin should be a show stopper.
Step 4: Check cage conditions. Cage should be free of dried fecals / urates. If there are urates they should be snow white and fresh. I just don't trust anyone selling animals they let sit in their waste, it is a bad sign!
Step 5: Know your vendor! Some vendors have a great reputation, some not so much. Bring your smart phone to the show and be prepared to research a vendor. I like Fauna Classifieds BOI for this. Some vendors can have good looking animals but have other issues with after sales support. And do not operate under the false assumption that just because a vendor advertises here they are always good. That mainly means they probably just aren't criminals. Exceptional vendors will have things like entire threads on here devoted to their babies people have bought over time...
Step 6: Trust your gut! If you look at a chameleon, can't find anything wrong but something is telling you not to buy don't! Your subconscious will pick up on things you won't. This may sound crazy but I personally have regretted every time I ignored that feeling...
Step 7: Buy a Chameleon and post pictures here!
Hope that helps at least a little...