It can make it harder, but if you need something for a mog just roll need on it. You can try tacking on an explanation and some courtesy, but at the end of the day it comes down to the no-trade thing, so you better roll need if you want it, and If you get kicked for being a "ninja" don't let it bother you. This especially happens in Deadmines and Ragefire Chasm, where you'll be rolling against lvl 15's in whites, and many just don't care that there's a 35% chance of getting a much better blue item than the +1/+1 green you've farmed for months, and will kick you without giving you a chance to explain why you're rolling need on a +1/+1 green with stats you don't use.