Gold sellers have already pumped too much money in, so it's lost all value. Legit players who didn't buy gold/get lucky as hell/farm their fingers off get screwed in the long run.
I highly doubt banning all the gold sellers would have an immediate effect ( economy wise ) but it would help.
Some of it is just stupidity though. Some guy thought every purple weapon was ridiculously expensive. Level five purple katana for 1.5 mil? What? I'm happy I found this one reasonable shop filled with stuff I needed. Found a GBL wand for 50k, and a bunch of other things.