I've been told many times over by pro musicians that it's a major bad to
ask to sit in, or even to hint around or "chum up" with that intent.
That's why these folks are often anti-social - any time a stranger comes
up to them they know what it's probably about - they want to sit in and
it's just a matter of how much BS they are going to sling around before
they get around to the strong hints. The 'higher' level the gig and
level of the audience, the less likely this is to happen. A polished
national act like Little Charlie and Rick Estrin?? Forget it! These guys
are polished pros and I'd say never in a million years are they going to
let someone they aren't familiar with sit in on their gig. I saw them
last week and Rick was pretty rough with the audience members who were
even requesting songs, so I'd never dream of approaching him, haha. But
for example, a townie band playing at the local watering hole, maybe
they will just on a lark. I'm not talking about that scenario. In fact,
in one case I was in a dump place and a townie band was playing, I was
just talking by chance with their guitar player/leader on break and he
asked if I played and I said yeah, harp. He said they do Long Train but
do the harp solo on the keyboard and asked if I wanted to do it. I said
what the heck, I know the solo, but he asked first could we go out back
and I'd play it for him. Only then did he agree to go forward. So
sometimes it's a crap shoot. But in almost all cases, any band getting
paid for their performance will not take the risk - if you get up there
and blow it, they are going to be the ones hearing it from the club
owner and their reputation will be harmed to the audience because it was
"them" who sounded bad. The pros I've talked to (Jason Ricci is one,
Carlos Capote another) said the things they hate at a gig are:
1. People who ask or hint strongly to sit in (or have their girlfriends,
etc suck up to the band to get them to do this)
2. People who just bust their harps out from the audience (or worse
dance floor/stage front) and start playing (worst thing to do of all)
In short, don't do it. They'll put you in their mental 'bozo bin'.
Unless you are someone who they recognize as being 'worthy', i.e you
must already have a big name and they would recognize it upon your
introduction.