Google provides a pretty easy way to manage your security. If you go here and log in to your Google account you can change the way your info is being used. To the OP you can remove that Google login to eBay here:
https://myaccount.google.com/security
Scroll down to the bottom to the section that says "Signing into other sites" then click on eBay and a "remove" button will appear. In fact, you can even turn off that "feature" completely here.
Likewise the links on the left side will allow you to control a lot of things in your Google account including how your data is used.
While I am no means an expert on such things, with the proper precautions I'm comfortable with the way Apple and Google handle this stuff, at least in my use case.
On the other hand I would NEVER trust Facebook. Period. Full disclosure I do not have a Facebook account, though I did create one for my dog for friends and family to share stuff.