The problem with Mercari is that people expect things to be dirty cheap and don't expect authentic, so genuine
gucci bag won't sell for $500+ in a week or 2 as on other webs. On posh and tredesy, one has the state of mind, that items are in most part authentic and isn't surprise to pay premium, same as buying from realreal or
fashionphile. On ebay, one knows it's mostly gamble but still the general approch is positive as various deals and original items can be find. Because Mercari started "small", selling small samples and cosmetics, little t-shirts, cheap penties, I think it had big impact how it's being proceed overall.