Once at a reptile expo I was looking at some corns that were as thick as ball pythons, if not more. The corns were obese, so obese that it was hard to look at them because they were truly grotesque. I consider that to be "scumbag power feeding" at work.

On the other hand, my yearling albino female went through a phase where she wanted a small rat every 3 days, and I let her have them.

As others have said, it is species dependent, and situational. If the breeder is not putting the health of his animals first, I would not buy from him. If any of his animals appear to be in poor health (either obese, underfed, or otherwise ill) I would not buy from him. I simply move on to the tables that have healthy, attractive animals.