I had to call ebay tech today regarding an issue. It was just a question and I didn't want to go through the verification process so I did not provide my ebayID. The Indian lady kept asking for it and I kept saying I don't see why that would make a difference as I was experiencing a functionality issue with the site.

Then she spilled the beans. She then said "That way I can see what you are looking at." This kinda freaked me out. I asked her to explain. She then said "So, that I can see your navigation history. See what you are looking at right now, what your previous results were, the listings that came up and what they looked like to you including ads and suggestions." I then asked her how she would be able to do that unless ebay was keping a history of everything I am doing while logged in. She boldly then said yes, they are. It's in your user agreement that you agree to let ebay do that. WTF!

So pretty much ebay is doing a giant big data on your profile. If you are logged in while you shop every word you type, every movement of the mouse, the way you type, browse, what time of the month, how much you buy, all of that is being stored permanently!

If this bothers you, I would recommend clearing cookies, then making sure you do all your browsing "not logged in".