I hate ebay, in part because of the constant begging for positive feedback.
Now I'm getting it from Amazon's sellers. Every purchase that's not from Amazon itself results in emails asking me to leave positive feedback, reminders that if I haven't left feedback I still can. I got tired of that pretty quickly on ebay. "A+++++++++" seller
There's also the "used book scam" which has hit me twice. Find a relatively inexpensive copy of a rare book. Order said copy. Copy ships. Copy never arrives. "So sorry, it must have gotten lost in the mail." Next day the same seller has a copy available at 3X or even 10X the price you paid.
It appears that they get "seller's remorse" and pretend to ship you a book (with no tracking, of course) and then miraculously find another copy they can sell closer to the prevailing rate. Several sellers seem to have a lot of feedback that implies this is what's happening.
The third scam I've seen is the "I don't really have the book, but I'll have someone else ship you a copy"