Is there any fair means of determining wow gold whether you should invite potential loot competition to a group? Is it right to turn someone down for a slot because they need the same drop as someone who's already in the group? And does the situation change if a group member's been after a drop for a long time with no luck? Is it really all that right anyway for people to "call" certain drops as their own before the run even gets started?

Yes, life would probably be a lot easier if I didn't PuG and stuck only to guild runs, but I actually enjoy pugging. It's a good way to meet new people, and get information and gossip from around the server. And if I didn't PuG, I would have no awful PuG stories to write about here.
That said, there's no sense holding up a run for any amount of time because you're stuck trying to find a leather wearer for your picky mage/enh shammy/DK/resto shammy group. Competition is a wow gold part of playing an MMO, and when all things are said and done, WoW is one of the least competitive I've ever played. Anyone who knows what Byakko's Haidate are will understand me here.
I try to comply with my group members requests. I don't beleive I kicked someone to avoid competition on drops(as in the past most gear i wanted was dps offspec since i was pretty geared); however, the only times I did NOT join a group was over the Sun Eater from hMechanar and The Red Sword of Courage from hUtgarde Pinnacle. Both people who pm'd me asked me if I wanted to go and told me they wanted the item and was dpsing till their set was good enough. I've run hUP 23 times for that sword and for hMech I NEVER saw that sword and have been exalted with the wow gold Sha'tar many times over, I told them that and I'd really really really rather not have the competition. Knowing my luck, it will drop and id lose it. The last few times ive had to roll for anything ive rolled in sequence a 2, 9, and a 3.