As a (hopefully humourous) aside.
In the 70's I was involved in the running of a Folk Club. (Standard pattern, Residents, Floor spots, and then the Guest).
On one particular night. we'd managed to book a pretty well known artist to play. On arrival at the pub, there was this young chap with a guitar, who'd travelled 50 miles to come. He asked if he could play. Of course, we said.
Well he did a couple of songs in the first half. Nice voice, Good guitar technique etc.
So when it came to half time, we asked him to do 3 more songs as the "support" to the guests 2nd set. (After all he had done a 100 mile round trip, he was pleasant to listen to, and it meant the rest of us could have the rest of the evening off!).
He was delighted.
The time came, and he did three songs, all of which was material popularised by, you've guessed it......The Guest artist!!!
In fact, they were going to be the climax to the artists 2nd set!
(Sound of ripping up setlists at this point!)
It's not always incompetent performing that is the problem. It's sometimes thoughtlessness on the part of the performer.
The guest seemed to take it in good spirits, but, I'm sure he was seething inside.
PS. The guy actually asked us to book him for an evening after the show. We reluctantly declined!!!
(Oh and Rosie......Panini Blandness.....Priceless!)