It is really hard to enforce any kind of rules for this kind of stuff. You can say they look small but you cant prove it. The seller can say I don't feed that much that's why they are smaller.
It is really simple thou. If it looks to small don't buy it. That's why there are many vendors go and look around and pick out bigger more active animals. Also you get what you pay for. If some one cheaps out to save $10 what can you do if it doesn't make it. Mark it up as a lesson learned, we have all been there at one point.
WALTER @ Mice & Things