By my experience with I ebay.in I can surely say that the products listed by large numbers of sellers are not 100% original.
For example if you want to buy a nike shoes there is 99% chance you will land on a page listing a copy of the original product.
As far as I am concerned I would suggest ebay to list authentic products so that the customers have more faith and can buy without any concern.
And the worst part is their return policy it takes a hell lot of time.