I would imagine the snake would go to a bigger weight with 1 feeding as most hopper mice are about 12g. I know because i have to pay close attention to my baby Pokigron Suriname girl so she doesnt eat too big of meal and puke.
And like i mentioned above, most wholesale reptile vendors dont care really about the animals. It's all dollar signs to them. And maybe they are selling of the healthy weight or visual ones on Morph Market because the pet shop you work at doesnt want to pay the prices they are asking? I know a lot of breeders will sell their normals or stillborns off cheap to people who have snake eating snakes.
And welcome to the world of animal trade. Puppy mills, whole sale reptiles etc, it's pretty much flesh peddling except where as human slavery was abolished for its cruelty and inhumanity, the pet trade isnt so much and even less for reptiles.