+1 to what earthygirl said on eBay and Tradesy.
eBay: I sell (and buy) the most often on eBay, primarily because of the low(ish) fees. While it’s more work to do it yourself, they do have decent seller protections in place. I once had a buyer say they didn’t receive a bag & request a refund... but bc I did the postage/tracking thru eBay (and it showed as delivered), they handled it 100%. My main feeling w eBay is as long as you can take decent photographs and aren’t trying to oversell on condition, you’re most of the way there!
Tradesy: sold there years ago but never again, primarily because of their return policies. Back when they would take back/sell returns, I had a buyer return a Proenza bag which Tradesy then sent back to me claiming it was fake. I assume it was bc their team was looking for reasons to not have to handle the volume of returns (and my friend @ Proenza was v amused to hear the bag she got me was “fake”).
Poshmark: I also sell (and buy) a fair amount on Poshmark. It’s nice to just get a shipping label when something sells and be able to use any packaging, but I have to set my prices higher here bc of the 20% fees (with no cap, no matter how pricey the item). For that reason most of my “nicer” bags tend to move better on eBay. That said, it is nice that Poshmark calculates upfront what you’ll make on the price you set, unlike eBay where you get hit with their fees the month post-sale, and the PayPal fees quietly.
TheRealReal: Wildcard. I like buying from there (a little too much), but as a seller I’m mixed. The primary reason I will go
TRR over eBay is bc they’re able to get more for certain brands (like LV and Chanel) than I could on my own. Maybe it’s just me, but my sense is that some folks buying $$$ used bags (even for a relative deal) prefer the safety of an “official” business and would be willing to pay more for it there than on a platform like eBay, Poshmark, Mercari, Depop etc. where you’re dealing with a wiiiide spectrum of individual sellers. Currently I’m not thrilled with TRR’s communication re: my latest consignments there, I feel like they could be better at stuff like notifications that items were received / accepted. The fees they take are also tiered depending on your status/how much you consign -OR- what the resale value is if certain items. They pay you monthly, by direct deposit, check or site credit (where you get 5% more).
And that’s it for me... on the other sites you list I’m either a looker or buyer, never a seller (yet...)