The marketplace community desperately needs a competitor to eBay. They have practically no competition so they are free to do as they please no matter how unfair it is to their customers. The current fee for selling most things is exorbitant at 15% and just greedy. When I first began using eBay in 2000, the fee was about 3% if memory serves.
What also sucks as a seller is the inability to leave negative feedback for shit buyers, like those who bid and then just ghost you when it's time to pay. They just go completely unpunished and as the seller, all you can do is cancel the sale and relist. I also hate that they removed bidder restrictions sellers used to be able to set, like no bidders with less than x feedback, buyers with recent negative feedback, etc. Not to mention no matter the reason for the dispute, eBay will rule in favor of the buyer 99.9% of the time, and plenty of sellers have been royally screwed by dishonest buyers. It's way too heavy handed in favor of buyers.
However, as a buyer it's great. I find stuff on eBay all the time I'd have a very hard time finding locally, if at all.