Amazon's customer service is first rate, report the items.  Here is part of the seller's listing requirements.

Quote:
Please verify that this is the exact product you want to sell.
To list your item in Amazon Marketplace, it must exactly match the product you are listing against. Listing a different format or edition of an product, and noting the difference in your seller comments, is not permitted per our Community Rules. If your product does not exactly match the product below, please try searching for it again.

I usually use the traders present on the Amazon UK site, and so far I didn't have these kinds of problems. I have 2 traders I use very often - Moviemars and AllYourMusic.

I always check the feedback when I see a seller I haven't used before. Some of them get a bad score if an item takes too long to arrive. I don't see this as an issue. Usually it takes 2 weeks to arrive in Belgium, but on occasion it's 3 to 4, which is I suppose a postal issue and not a seller issue. Others get a negative score because their dvd's are R1 and the buyer doesn't have a region free player. This is a buyer fault. But if I find 1 entry where a customer had a problem, and the seller refused to anwser mails, and solve the issue, I move on to the next.