Permabanned
Sales yes.Do you work in the industry, or is this also speculation? Who is selling heavily discounted keys to whom? Are they selling them directly to the key sellers?
Because a lot of grey keys are ripped out of boxed copies of games in places like India/Brazil. There's been enough written about this to be fairly certain of it.
This is why you should use trusted sellers such as G2play through sites like Kinguin who categorise them as recommended sellers, Don't just buy from the cheapest available or else you could easily be buying from someone running a scam. But that's on you as an individual you can't blame the industry that's developed around key codes for that.
Every industry has it's bad eggs. Whenever money is involved there's people trying to make a quick buck.