You answer:

It's not that hard, all you need to do is find a reliable platform, and that's it. Well, I can tell you that it can actually be highly profitable, and I manage to profit by selling skins like <a href="https://dmarket.com/csgo-skins/product-card/awp-atheris">awp atheris</a> pretty often. I can leave a link to the platform that I use for that, and I'm sure you won't have any problems with that.