I have no experience except ebay but the top 8 are
Facebook Marketplace.
Craigslist.
Nextdoor.
VarageSale.
OfferUp (formerly Letgo)
Poshmark.
Vinted.
Decluttr.
and of course freecycle

For artists there are Pintrest, Etsy and of course Sotheby's which is potentially as corrupt as its competetors.