I wouldn't sell any of my bp hatchlings that small, nor would I buy one that small (unless the breeder was local to me and I knew them personally.)
In my way of thinking the breeder should really make sure they are eating consistently and not sell them until they have some weight on them. After being shipped and then in a new environment that could be quite different from what it was used to those balls could be at your house in a quite stressed state. Remember, it's not uncommon for new (to you) bp to not eat right away. Especially if they haven't had that many meals in them.