It makes no sense to try to make profit selling green, blue or red dragonscale items on allies side.
Selling theblack Dragonscale set has become interesting for the bonuses this set has become since the last patch (1.8): +1 to hit, +2 crit, +10 Fire Res.
Leaving epic items aside, this set combined with the stuff from Dire Maul is the best, UNLESS you have the complete Beaststalker set (look at the AP bonuses you get for the 7th and 8th piece.
So, selling Black Dragonscale is a very good option, as almost every Hunter will at least consider wearing it.