Selling gil is bad for the game as a whole and visibly hurts other players; doing it yourself wouldn't mitigate that.

Solution:
1. Make sure everyone knows that the reason accounts get "hacked" is gil sellers. Period. They're the only people who have an economic incentive to steal your stuff in an MMO.
2. Bans for buyers. No excuses, no sob stories. Bye.

Do that, consistently, and the problem will reduce to a tiny amount of background noise. Make excuses for players who think it's fine to hurt other players to get ahead, and you will lose out in the long run.