I really don't see the problem here. Yes, your Retainers only have 20 concurrent slots in which to sell things... but they have a full seven pages of Inventory space. I've recently run into this selling Velveteen when I hit lvl 25 and started farming Banemites... I put up three or four 3xUndyed Velveteen(HQ) when I log on, these sell in an hour or two, tops. I get the message, and the next time I'm in town I hit up my Retainer, Split off a few more x3 stacks from my x99 stack in my Retainer's inventory, and post them. I sell for 15% higher than the lowest price to counter deflation, and I make a net profit of anywhere between 8-10k gil/hour after repairs. As a Weaver I know from my Crafting Log that Velveteen is normally used in stacks of this size or slightly less, so that's what I post. *shrugs* Doesn't seem that complex to me.