Parasites can cause regurgitation. I worm every snake I get. Even from reputable dealers.
Over the course of the snakes lifetime it can easily be exposed to parasites and ingest them and have them build up in them. Conscientiously keeping the cage clean and keeping the snake from contacting feces or fecal remnents is mandatory to gain control over reinfestation and parasite build up in captive snakes. Any new snake you bring in, even if housed separately, can introduce parasites. A snake you have handled at a friends house, herp club meeting, show or conference can share the same. You handle it, there's fecal dust on it or in its cage. You forget to wash your hands, fecal dust or other contamination is on your shirt sleeves, then you handle another snake, and transfer the resistant parasite eggs to your other snake(s) etc. :awcrap: :bomb:
Live, not frozen, prey can act as vectors, introducing parasites into your snakes.
It is an acceptable and even recommended husbandry practice to worm new snakes. Captive snakes can build up unnaturally heavy parasite loads simply due to the captive conditions. Like being in regular contact with fecal dust or buildup of stools.
My two cents worth. Thanks