There are two sides, If you dont know, Sellers can no longer leave negtive feedback for buyers on ebay. when this change went through it back open season on ripping seller off on ebay. (feedback used to be a mutually assured destruction) kind of thing. once the seller lost “negitive feedback every buyer had 100% feedback even if they were professional scammers. So ebay came up with feedback extortion so if a seller makes refunding money contingent on positive feedback, bingo they have breaced policy (the same goes for buyers).
Shre shill bidding happens they buy each others stuff and say how good it is (and loose the transaction cost).
Also they set up account and get x numer of good deals and then try t cash in and blow out some too good to be true deals that never ship. I have no idea if ebay gets there money back on thoes but at least the buyer does (after 45 days).