Actually, you do. As a supplier of a proprietary product, you set contracts with your distributors and retailers that limit what they are able to do with your products. It's one of the reasons retailers throw excess stock away rather than donating it or selling it for super-cheap. Because their retail contract stipulates that they can only sell to consumers, not businesses, and they have to sell above (or below) certain price thresholds. This is fairly common practice across most retail stores.
For example, I once worked for a company that made a specific name brand hair care products. All of our distribution contracts had a no-resell clause with exceptions to specific trusted re-distributors and retailers. And different companies got different contracts. Because Wal-Mart bought our product in significant bulk, they got a discount on our margins. However, Wal-Mart couldn't turn around and use that discount to resell our product to, say, Target - who wasn't ordering the same bulk quantities and thus was not getting the discount.
This is done for a number of reasons, but mostly to discourage second-hand or 'black market' sales where businesses purchase in excess bulk quantities for the expressed purpose of reselling to other businesses who don't or can't get distribution contracts for various reasons and to limit the ability for knock-off, illegal or illegitimately acquired products to circulate amongst both legitimate retailers and grey-market retailers.
This works both ways too. As a retailer, you want to be a 'trusted vendor' and have direct contracts with your suppliers and distributors because you don't want to end up in a situation where you find out your products are illegitimately acquired or knock-offs.
