Even if it states on Steam Terms of Service that it is a violation, the biggest sites are open and Valve doesn't care.

Why it could be bad

Some time ago, sites gambled csgo skins from player to player through their api. Valve ignored it. They eventually made it clear sites couldn't do it anymore, but that was only after a lot of sites started using that feature to directly scam their users.

This kind of site, very specifically, got banned: "This is a trading site. You'll earn $100 in skins you can withdraw if you send us $15 in skins". You could naively send your stuff, but never get anything out. All of the sites of this type willingly shut down because they knew Valve would ban their storage accounts, regardless of being legit business or scams.

Why it's not bad

All of the other sites not involved with this were kept operational without any kind of problem, so valve clearly knows about it, but decided to ignore it, only taking a stance to the aforementioned sites to protect the increasing number of scammed players and scam sites abusing the same thing over and over.

The absolute, contextual truth

If Valve is okay with it, then I'm okay with it. I'll keep using Biskins as I described in my How to turn your STEEM/SBD into Steam games without ever feeling like I'm doing something wrong. Unless, of course, Valve decides to care, then i'll stop endorsing this practice.

Thank you for reading!