Buying and selling lawful and legal products through ebay is permissible.
Ebay provides a platform to individual and corporate sellers to sell their products online.
The case of permissibility of "buy it now" items is very clear and simple but buying and selling lawful items in a "bidding" format is also permissible because Islam allows sales through bids as long as they are fair.
However, there are some other websites where people have to purchase bids and once the bidding has an ended the item is sold to the last bidder.
I personally believe that this form of bidding is not permissible as it closely resembles gambling if it is not pure gambling.
The reason why I believe it is a form of gambling is because all the bids placed on a single item are paid for by each bidder. At the end the product is sold to only one bidder while others lose all their money. This is very similar to lottery where a lot of people are risking their money in wish of winning the grand prize but the prize is only given to one person or few individual while all others lose everything.
In contrast, ebay bids are free and there is no cost for bidding. Only the winner is required to pay for the item and other bidders are not required to pay anything.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America