Same as normal party loot. :( You get an announcement of what was dropped if someone in your party participated in the raid (usually, not always mind you - it's a big buggy) and then the drops get prioritised to the group that did most damage (which also got most experience, yay!).
My alliance has a DKP system set up, and you buy raid loot based on your point count. And in our case, it's need before greed. That is: if I need a Tallum Helmet, I'll get it before Joe (who just wants to sell it for the almost 200m it's worth).
What Maline said, no system really, not anything built in the game.
In reality it depends on your clan/rules really. Most have a "need before greed" set up though. You aren't allowed to buy something for low just to turn around and make a mad profit, if it's some useless item it's either crushed for crystals or sold to buy something someone actually needs. No one raids without rules in place ahead of time, of some kind.
Blah. When we our parties to have nukers in ever group, I got about 250k EXP. Still, I won't complain. Getting crappy EXP was how I got my Majestic armor mats.