Well, Tradesy is a series C (late stage venture)- and most fly by night operations don't ever make it to series C. Once you get to series C, you are a viable entity.
The companies that went out completely are Vaunte (the thing founded by Gilt), Shop - Hers (bought by Tradesy) and the like. Vaunte had $2 million in venture backing, Tradesy has $75mm, Realreal has $175mm.
I don't know why Tradesy tightened up on payouts or commissions, but I suspect it is because Poshmark suddenly is claiming to be profitable, tradesy is probably under pressure - but that doesn't mean they are going under.
As far as glassdoor, that is a vehicle for disgruntled employees everywhere. Thredup is the worst.