Ebay used to be a service where people sold their used stuff. Now it's turned into a chinese-made product retail sales outlet. There are still a few private sellers, but nothing like it was years ago.
And PayPal turned into such a money-maker they sold it off. As an ebay seller we don't even get paid by paypal anymore. I have a product I make and sell on ebay - at least it gets some exposure traction with buyers. They take ten percent which I think is a lot.
Many retailers on amazon also sell their same product on ebay. If they have something I want I will usually try to find their direct website and buy there, bypassing the resellers if possible. Much as I love the convenience of amazon, I loathe the way they squeeze sellers and competitors to death. My primary business occupation is in the office products sector, and our main competition has changed from Office Depot and Staples to Amazon. Like Walmart, they decimate small retailers, taking over and dominating entire product sectors.
I would rather buy from ebay than amazon where possible. I've never had a problem getting product or satisfaction. And if you pay with paypal they do have some buyer protections. And if you pay with a credit card you do have that recourse as well.
I've had pretty good luck with Aliexpress as well, but hate the slow delivery, and you never really know if you have a valid or reliable seller. There are a lot of these sellers that also sell on Amazon - more and more direct from china sellers. Ebay too. I always try to buy from a US based outlet - at least you don't have to wait a month or two. I like that ebay tells you where the product is shipping from.
I don't really return stuff. I keep a running cart going on all online sellers, and pull the trigger when something in the cart gets a raised priority.
If a retailer runs an abandoned cart reminder program I'll completely unsubscribe from them. I run an online store for my employer, about a half-million a month in orders, and loathe that kind of marketing. If an online seller sends to many advertising emails I unsubscribe from those as well.
Just don't bug me, emkay????