I start my BP hatchlings on rat pinks. I think they put out a great heat signature, they wriggle in a nonthreatening way and I rarely ever have to offer anything else for the first two feedings to get hatchlings to eat.
Of course you'd move up in size but also remember that a new owner often mis-hears stuff or asked someone else, or thought "mice" instead of "rat". Or the breeder didn't want the new owner to over feed the snake to begin with, and recommended a smaller size. Or what a breeder considers a 'weanling' is smaller or larger than what someone else considers a "weanling" and so on.
Sure, in a lot of cases, it's literally a lack of research or a seller telling the owner a small prey item because they maintenance feed. But it's not always. The people who owned one of my monitor lizards were feeding him a hopper mouse once a week because way back 7 years before when they got him, they were told he should eat a hopper mouse.