About epic gems I found that at least before patch 2.3 you could put a soulbound gem in a BOE item without the item becoming soulbound. I sold a healing belt with the
[Royal Tanzanite] from heroic Slave Pens without any problems. Jewelcrafters could potentially use that to sell their cheap epic gems to people who had stuff crafted, although I'd try it out on some cheap item first; they might have fixed that in a patch by now.
And of course they are unique-equipped so people could only use one of each.