Only thing about this is that then someone will come up with the idea of trading guns. And then everyone who spends iTunes galore will give their friends pbps. And then most of era will have weapons over 40k. Not that that is a problem, because then era would have to make a larger map to house all of the Pkers and basers.
The fee is iffy imo. Like, what if you were trading 100 shells for icy dagger. With a 200g fee, it would only leave you with 100 gralats. Maybe different items have different fees? Or different amounts have different fees?