I think this works in theory but the playerbase like you said would get a bit annoyed. Plus, you'd end up seeing a lot of gil move through the auction house to transfer between characters. Essentially RMT would use a Retainer to place a really basic item at an absurd price and then the character with the money would buy that item, thus transfering the gil to the RMT. Further, to sell the gil back to the players, the player would then place another basic item on the markets for an absurd price and the RMT would then buy it to transfer the gil. Yeah they'd get double taxed on it but they'd still be able to move money.