it begin to have abuse at the auction with powder sold almost at full price with only one charge left. I think only full charges powder could be sold, or on a different tab, or the price sorted by current/charge to put the cheapest first.
I think a good fix would be to list "price per charge", which I think is actually a great idea. There's probably more than a few novice players who wouldn't mind paying a couple hundred currants to check out what powders can do, but full price for a full bottle is probably out of their reach...