The Steam Deck has essentially enabled money laundering through Steam. Before the Deck, if you sold skins on the marketplace you could only use your Steam credit to buy games on the platform, or you had to do a shady 3rd party Paypal exchange. Now, you can use your Steam credits to buy a device with value that you can resell IRL.
Before that, you could also buy the Index VR set, which probably aren't as liquid as a Steam Deck. I won a Dota chest that could only be acquired by watching tournament games in-person, and after letting it appreciate for two years it nearly covered the cost of an Index. I was thankful because I had no idea what to do with hundreds of dollars in Steam credit.
I think most people are fine with the “shady” selling sites when it comes to laundering. I sold my CS inventory a week ago (lucky me!) and I had no problems with getting the cash. Reselling steam decks feels very inefficient
If you are in that business the question isn't really if it's against the rules or not, but if it's possible. You can use your in-game currency that you've gotten through whatever means to get a physical product that you can then resell for cash.
