Well the person who put the shard up for roll has a say in this as well. Just say ask everyone who plans on rolling for it and include no "buddy rolling".. Your loot, your rules...
There has been many times I seen people roll on items that another char can use more and I didnt count their roll and gave to accordingly. Like TOD rings, i saw two pallys roll on a ppally ring that dropped for me and others rolled on it. I looked to see if they were pallys and what level etc... forfeitted the others and gave to the highest pally. Did it also for a two rogues rolling on a icy raiment and a cleric rolled on it. I discounted the cleric, who incidentally was just getting it to TR with, which I appreciate but the CURRENT light fighter types needed it more.
If it drops for me and a guildy wants it, its theirs, multiple guildies roll...