Yes, look out for thin or bony animals, because no-matter what the vendor says if its thin or {bony} its probably not eating well or possibly they have only maintenance fed their reptiles, make sure the animal has clear eyes, {and im not talking about being in shed} make sure it is alert, watching your movements, hands, arms, fingers, but be careful as you may get bitten! I would not buy a wild caught ball python unless you are an experienced herper, the only way to know is to ask!if u can get them to do it ,have them open the mouth of the reptile to make sure there is no mucus or dis charge in their mouths or nose, interior of mouth should be pink-ish coloration, and also check for mites, look in their water dish before you handle the animal, and check your hands after, will look like specs of pepper, in the water or on your hands, and one more thing, check for ticks, yes ticks, they are very hard to spot when they are small, and they match the coloration of the ball python brown very well.
Well good luck picking out your new pet but remember, while most vender's are honest people, there are still those out there that will try to rip you off so try and stick with vender's u know or have at least heard of and ask about return-refund policies, if they don't have one BUYER BEWARE!
Hope this helps a little
Kris