Q: Can ferrets eat bugs purchased from a bait shop or a pet store? If so, what kind? Would it be mealworms, crickets or whatever that are bred?
A: I would not encourage you to feed bugs to ferrets. You do not know what may have been fed to or sprayed on these insects. You do not know if they are safe for your ferret to ingest. Plus, you do not know the nutritional content of these insects; most insects are notoriously low in nutritional value for ferrets.
If your ferret gorged on these insects, it would be like feeding candy to a child and then expecting your child later on to eat a nutritious dinner. Ferrets may eat these low-nutritional content insects, become full, and then not eat their normal diet. This could cause your ferret to become nutritionally imbalanced, leading to disease in your ferret.
As a treat, maybe you can feed one or two of these insects a week, but my advice is to find other, ferret-specific treats to give to your ferret.