This is really innovative but very wrong. I would never do this to anyone. When I used to serve I skimped a few people but I would never do this.
Anyway you look at it, you don't make a huge profit from selling. Unless you have a really good plug who sells cheap. But just remember, if you ever buy cheap bud it's probably shit. Though, some plugs get their shit from growers who sell dirt cheap and turn a huge profit.
Basically, these "methods" are stupid and could potentially get you killed.