Similar to the tabard selling, but perhaps a bit more lucrative, is to use the shards in the crystalforges at the forge camps, turning them into the flasks that are only usable in BEM and Gruul's lair.
you'd be surprised how many lazy people there are whos guilds are going to gruul's. that or people who are ignorant of the BEM quests and don't know where the flasks come from. a stack of melee flasks on my server goes for around 30g. 50 shards = 30g compared to selling the tabards which is 50 shards = 1.19g.
anyway, sell away