I think that it would be useful to have a key (shift) that a player could hold down while clicking on a material to transfer 10 of that item to the trade window at a time. This would certainly make selling, say... 500 gel drops a good bit easier.
I know the 500x trade doesn't happen all the time, but I routinely ask for 50 or 100 of a low star material for crafting purposes.
Without question, I am all for this one. I get so used to using shift for Crystal deposits that I get confused when it doesn't work for Trade, heh.