Interesting thread!
There is a fine dividing line between disappointing the audience with a poor performance and disappointing the audience with a no-show. Both can get you a reputation for unreliability. I don't know which is worse.
The only time I have ever missed a gig was when I had laryngitis and couldn't even croak a note. A particularly severe bout struck a week before a singing gig. My partner rang the organiser to say I would have to cancel, but hoped that with a week to spare she could book another act and warn the club-goers that week there would be a change of plan. She was completely unsympathetic, and suggested I try antibiotics rather than cancel. Needless to say we have never been booked there again. And it was a gig I really wanted to do!
Had we turned up there we would have given a completely unacceptable performance because I had no voice,and croaked like a frog. The audience would have been ( understandably) annoyed at the standard of 'entertainment ', or would have possibly not gone back to the club in future weeks.
Mary