^^ Ebay is absolutely trustworthy. Trustworthy, even though it's not selling anything, it's still a platform for buyers and sellers to interact and buy/sell products.
There are people who sign up as sellers and list their products on Ebay. Ebay just promotes their stuff for a small fee (aka. commission) from the sellers, which is usually a small part of their stuff's selling cost.
As far as buying from ebay is concerned, you need to be extremely cautious. There are different sellers selling same stuff and the prices may vary extremely from seller to seller. You need to have knowledge of the current market prices before buying stuff from there.
Also, you need to be cautious about some specific terms used in selling stuff there. terms like like new, * company * OEM, etc. Apart from that, you can keep a screenshot/print of the listing of a product you've purchased or are planning to purchase, as sellers have the right to change product description.
Before buying, a check, of the seller's ratings (aka DSR-Detailed Seller Ratings in ebay terms), buyers' reviews(available on his shop), is a very helpful thing.
As far as Ebay's payment policies are concerned, they use PaisaPay for transactions for below Rs. 10000. In this payment method, the seller wouldn't get the money, till the time you haven't confirmed receipt of the item. Moreover, ebay maintains a strict item delivery time, within which, the seller is required to ship the item to you, else, you get a full refund and the seller will incur losses in terms of shipping charges+ebay's penalty.