If you dont like what you're getting, then by all means switch. If you're not comfortable with their service, switch to another.
However, all animals deficate when they are killed, that's really nothing new. When they zap a cow in the head with a big jolt of electricity, they crap all over themselves. That's exactly how e.coli gets into the meat, gross but true. I dont know that I'd be overly concerned about your snakes ingesting a little mouse poo---because they're certainly ingesting whatever poo is left inside the mouse when they eat it.