While I'm not sure that the game needs the ability to buy partial stacks from the boards, I would absolutely LOVE to see retainers able to both buy and sell. Its one ability that has been missing in the game that it really needs.

You're mistaken if you think that will set a floor on board prices though. I've seen people selling stuff for 1 gil on the boards, when simply selling it to their retainer would have netted them 35. Granted, in this day and age that difference, 34 gil, is pretty much meaningless, you would think that the "dump on vendor" price would be the floor on the boards, not 1 gil. I really don't see a buyer section on the board bringing the floor up.