I remember them saying a while ago that the raid leader has to explicitly state the loot rules before they can do anything, as in state them so that there is no doubt on how loot is decided.

I.E, saying "we're gonna roll on loot" isnt enough - it doesnt specify enough for them who wins. Common sense dictates the highest would win, but there needs to be a "and the highest roll will get the loot" for them to be able to act. Otherwise the master looter could argue that the rolls related to something else, and he uses a different system.

Good raid leaders in pugs which are raiding content where people will want drops will usually spell out the loot rules clearly before your first trash pull. If they dont, ask them to. If I'm joining a pug because I want stuff from there, I generally leave if they dont, especially when asked.