Selling Windows OS

I see people sell Windows on other sites such as kinguin and bonanza, bonanza doesn't let you sell Windows unless you use PayPal as the check out method, but isn't it against there policy to sell Windows keys? Seems some people have been selling for awhile, I'm just curious if there is any way to do this without getting banned

www.bonanza.com/booths/Ifixitall pretty epic. this won't even pass on german classifieds sites. perhaps bonanza is still relatively unknown?

Business idea: go on taobao, get the licenses for $1, sell them for $15. wow.