I wouldn't. There was a dev ( I forget which game, but def indie ) that said the pirated keys from those dodgy sites actually ended up costing them money, and they would've been happier if people just pirated the game instead if they really didn't want to pay for it.
I think it had something to do with credit card fees
Edit: found this on reddit
Grey Markets are often done by credit card scammers which results into chargebacks by the credit institute resulting in processing fees for the producer of the game or even getting them cc banned.
In before someone tries to guilt trip you for that because "developers aren't getting money from stolen keys" and the developer isn't an indie developer but a studio owned by Microsoft or EA...