I'm recently back from Saltburn, where I went to see Grace Notes three (or was it four?) times, so I guess that makes me a stalker. They didn't seem to mind. They didn't do complete repeat sets, just a few favourites. My wife was doing something similar with Nancy Kerr and James Fagan, so when she came to the last GN set I was able to pass on the good news - Witch is back in the repertoire! Then they didn't repeat it....

There's no ideal way, but as an audience member I'd agree that complete repetition should be avoided if possible. If I see two identical sets, I'll tend to avoid the artist in the future (at least, the near future.) I suspect that the more varied two different sets are, the more likely I am to go to a third.