First of all, a "crypto Ebay" would not be feeless. Handling with Bitcoin costs always fees.
Secondly, crypto Ebay's already exist in the Dark Web. There you can find many marketplaces and Ebay clones where you can buy all things and stuff (legal and illegal) with Bitcoin and cryptos like Monero.
Maybe OP didn't know about it or had forgotten about how crypto became famous in the dark web for something like that,
And we still carry it till this day because some still see's crypto or Bitcoin only as a money for illegal activities because it was once known for that purpose.