What kind of logical fallacy is being used in this passage: the trouble with pet shops is that they get their dogs from puppy mill.

I don't think that it falls under the main fallacies, but it is an assumption that all pet shops user puppy mills

The kind of logical fallacy is being used in the passage is over-generalization. Since, the author tries to argue that all pet shops get their dogs from puppy mills which shows fallacy because we all know that his claim is not always true.