This site does that and more.

It has a number of tools for checking up on eBay buyers and sellers. You can also see their feedback ratings.

Want to compare the feedback a seller left for a particular buyer or vice versa? There's a tool that will do just that. That's handy if you have a question about feedback left for a particular user.

There's more to the site. But the best way for you to understand what it does is to try it for yourself.