After bouncing between a few platforms, I've been using https://dmarket.com/trade-csgo-skins for the past few months with pretty good results. Their security system is solid, which was my main concern after hearing so many scam stories. I like that you can see exact pattern indexes and float values before trading. Started with just a bunch of random skins from old operation drops and managed to trade up to some decent plays and a knife. Their market analytics tools help identify good deals too - you can see price histories and trends. Not perfect, but definitely better than gambling on cases or risking trades on less secure sites