Buying used

I’ve been trying to buy more used clothing from places like Depop, Poshmark etc. vs buying new despite focusing on natural fibers. I’ve had success with some but I recently bought a top that didn’t fit correctly (small breasts but large rib cage peeps wya). How can one avoid this problem in the future ? Like obviously try to buy brands you know how they fit but I guess what if you want to try other brands or maybe you see a top that you love and it’s your “size” but you don’t know if it will fit since you’ve never worn that style brand etc. Do you just take the risk and hope for the best and if it doesn’t fit resell for you you bought it for or take a L and sell it for less cause you just wanna get rid of it? I imagine I’m not the only one that has struggled with this.