We had a fairly big (for us) outdoor gig a couple years back with a band we built around a singer. She backed out at the last minute for 'personal reasons' and we had to grab and hire some people and go on with a show. The guitar player we hired had his own band and ended up scarfing up the gig and took it away from us and we never got it back. His band still plays it (it was a concert in the park series show for a local town).
Long and short of it is that:
You almost never refuse a paying gig
There is another pro band that will take your gigs if they can (understandable)
Performers (singers, players, etc) that back out on gigs get a rep fast & I think nobody in their right mind wants to ever work with them again
To combat this we have players and singers we know sit in with us at gigs, with our own internal goal of seeing if they might be a good sub if ever needed. Not everyone gets this and I have had our own singers or other band members in our band not want to have outsiders sitting in.
I personally file it under the "doing good business" heading, meaning some performers do and some don't. The ones I think do not "do good business" I don't work with. Often the ones who don't are quite successful, so there is no moral to the story, just a personal code for me.
On the other hand, I once was hired to pay bass on a local yokel country album and the producer/engineer took an instant dislike to my BC Rich bass. He tried treating it like a P bass at the board and it sounded like crap. I was let go in an somewhat unprofessional fashion and another bass player in the wings with a Fender was brought in. A year or two later our band did an album for good money and this same person was brought up to be the engineer. I refused to work with him and we went to another studio and did a fine LP. That same bass that same year was used by me to record a song that went on the become a hit in Hawaii, so I know it was a great recording instrument.
"Music is a long dark dirty hallway filed with pimps, pushers, cons, and crooks. Oh, and there is a bad side to it as well"