Extra retainers, if you craft and sell alot, is one of the best ways to make a TON of Gil. I have 8 retainers on my main that are always fully stocked, with lowest prices on MB. I also have several alts with some retainers for a total of 36 retainers, each with fully stocked retainers. It's good for an easy 3-8m Gil a day in pure profit, just from selling stuff, no ventures.