Personally I'd like to see another sink from the market board in the form of an upfront fee (% of asking price just like the sales tax) paid whenever you put something up for sale or change the price within xy hours of the last time you changed the price. I'm sure there's some issues with this but ideally I see this mostly affecting people with many high cost items items who routinely change their prices to force poorer players out of certain markets to gain monopolies, people who usually don't put too much effort into making gil and just put stuff up and forget about it until it eventually sells wouldn't notice much of a change. As an additional benefit it might serve to make the economy in the game slightly less volatile