MMmm. I am a singer principally, and a poor concertina player. If I am singing in a concert or a singers club then I appreciate, but don't necessarily expect, some respect. After all, it's my job to sing the song in such a way as to cause my audience to want to listen. But in a session I tend to assume that the idea is to do 'joining in' stuff. Most musicians let me jam in, bum notes and all, with tunes I can only half play (albeit I'm drowned out by eight melodians anyway!) so it's only fair for me to pick songs I'm not precious about and to sing them in a key that enables people to join in. The experience may not be my preferred one, and the musicians will propably not hear my favourite songs, but we all get at least some enjoyment for the sake of a bit of compromise.