When shopping on eBay there can be issues at times with the sellers sending you what they offer. I've purchased a few items on eBay and I've always gotten what I ordered. However, I know a few people who had problems getting the items delivered to their home and they had to go through the hassle of getting a refund. This is an excellent platform and normally there aren't a lot of problems on it. The items normally sold on there are used, so a lot of times you can find a good deal on something that you're looking for.
Amazon is one of the largest online shopping stores and is trusted worldwide by billions of people. I actually like Amazon and will buy most of my things from this company. I have shopped at a few other online stores and have never been disappointed.
If I'm looking for a new item, I'll shop on Amazon. However, if I'm looking for an item that is no longer available, I'll go to eBay to find out if they have it. I needed a watch last year that was no longer sold anywhere online. I knew it would be a used watch, but I had to find one. I did find one on eBay and when it arrived, it was like a brand new watch.
This will depend on what you're looking for and if the item is discontinued or not.