I dislike the whole need for your class only thing. I realize its to counter ninjas but sometimes its just retarded.
For example, I was on my resto druid healing on heroic Forge of Souls. The last boss drops a cloth chest that has stam, int, spirit, crit and spell power. My current chest is leather chest with those exact same stats (its like the 3rd best chest from Ulduar 25 or something for resto druids), from Ulduar. Even though the only other cloth/leather wearer, mage, didn't want the chest, everyone had selected "Disenchant Roll" and I was unable to click "Need" and only "Greed" thus losing the roll and having it be disenchanted.
Totally lame.
At that rate all you can do is ask said caster to need it and then trade it to you.