The informal 'hands-off rule unless buying' isn't really about you & your snakes...it's really to minimize the stress of the animals being sold, and the risks to THEM
from you & every other person that wants to get their hands on them. Pretend mentally that you're a seller: would YOU want ppl that just handled other snakes
on the table across the room whose vendor you don't know & that may have mites or other diseases to be handling YOUR clean & healthy animals. I wouldn't.
Pet stores aren't the best place to buy snakes, but it's also where they are not so particular about this: they hope you handle & fall in love with & buy the animal.
Mites cannot hide on bowls, but germs can: wash thoroughly. Branches, yeah, I'd both spray (w/ diluted disinfectant as used on cage wipe downs) & bake 'em.
Some do negotiate prices...better to try late in the day & especially on the last day of expo (if a multiple day event). Depends on the seller- better chance if buying
more than one.