If you were selling CS:GO skins in bulk on a third party website for real money instead of the Steam Community Market, how would you check if it's safe? My first guess is reading reviews about the platform on reddit. But it doesn't seem to be the best way, because people tend to leave negative comments more than positive ones and after reading them you may even lose the courage to sell skins at all. So, what are the other ways to make sure that the website is reliable?

Trustpilot, general reviews, what streamers/youtubers advertise is usually pretty decent and reliable because it's their reputation on the line.