The only legitimate problem here is that the sales are not permitted (neither by law, nor by ebay policy).
There is simply no legitimate basis for the manufacturer to prevent subsequent sales of its product by a retail purchaser. Yes, obviously it's in their interest to protect their brand identity, but that's just not how selling something works. If they want to enforce something like this, they need to arrange a contract in advance. This is what they do with distributors, and why they have control over the terms of distribution. If the sale is legally permitted, they are no longer party to the transaction.
The only valid exception I can think of would be if someone is misrepresenting the contents of the bottle. In that case, it could be a trademark violation.
Note that there have been some absurd laws/court decisions involving importation of copyrighted works into the US---IIRC, a high end watch maker successfully blocked grey market imports on the basis that their logo was copyrighted and copyright conventions gave them legal control over the import market. This is, IMO, plainly absurd, and in any case doesn't affect domestic sales.