If SE cares so much about people's gil, instead of having gil sink, I'd rather they significantly lower the maximum amount of gil that players and retainers can have at any one time as well as the amount of gil that can be transferred between players.

Examples:

Maximum amount of gil
per player (excluding retainer): 50 million
per retainer: 1 million
per direct trade/mail transfer: 100 thousand

Also, maybe set a maximum price for any and all items sold on the marketboard.