They can switch on the flag. And do warzones. Or go intentionally to outden and ilum. Enough options, no?
Not quite sure, I generally seem to be flagged 24/7 against my will. I'll do more effort to ID people before helping them out in the future, hope that helps. I do know for Ilum Heroics that with a group making everyone time-out the flag seems pretty hard, and usually take far more than 5 minutes. And we usually end up with some people flagged anyway since we all get tired waiting.
Well, than you're luckier than I am. Tanks and healers can be hard to find. Non-flagged? Even worse. It's gotten a little better since finding a guild though...