I don't really have a simple answer to this. I have met this problem in many different kinds of music over the years. For instance, at a bluegrass jam session, where there are 10 musicians, 7 of which are guitarists---including me!

Some of these jams I ran, when I was a session leader for our local bluegrass club. Even then, it wasn't easy to resolve. Some people have one or two formula accompaniments that they use, whether it fits the song or not.

I have tried a) politely asking everyone to keep the volume down, especially if they don't know the song...

b)Asking people not to play the MELODY loudly while someone is singing.

c)Sometimes I would play in a key like Gflat or Eflat WITHOUT a capo...usually this would delay the onslaught of wrong or off-tempo chords...

d) This one is mean, but sometimes, I would fake chord changes during a song, and watch the fingerboard hawks try to figure out what chord that was...This is only effective when the wall of sound hides everything anyway.

What I do now, is sometimes ask people not to accompany me when the circle comes round to me. Or I deliberately choose to sing an un-accompanied tune. AND make it clear, that it is NOT to be accompanied...

Rich McCarthy