I'm not sure they are drop shipping, the items I have received that look like they are from Amazon appear to be from sellers that sell the same items on Amazon and eBay.

The fact that the items are delivered, sometimes, the day after an ebay purchase is why I don't think they are being drop shipped.

It doesn't really bother me so long as I am buying at the cheapest price. I check both Amazon and eBay before buying.