The problem with your theory here is if you choose to distribute someone elsde's creations in real life, if you want to sell five of them you ahve to buy five of them from the original source. What you are doing is buying one and they only get a one time price for it. You take it and make as many coipies as you wish and sell those competing with the original creator. Now if you make a deal with them allowing them a certain percentage of the gros income per sale I am sure there'd be rersolution, however what you are doing atm sounds very akin to the same thing we find in a certain overstock store in SL, and prety much just constitutes theft of other's creations and work.
Dmitri, I think you misunderstood the situation here. The OP does buy every single item he re-sells. He's not copying anything. The creators haven't allowed full copy/full transfer rights to these items. That would not be wise. and if they had, it would be within the rules (but not very nice) to copy and sell the copies. As he's doing it, there's nothing wrong with what he's doing, IMHO. Personally, I'd communicate with the various creators before I resold their work, but that's the only think I'd do differently.
OP, sorry you ran into a stinker. Sounds like what you're doing can be very beneficial for both you, the creators and the SL community at large.

