I've met people, called fans, going to a Rolling Stone concert and never noticing that Mick Jagger is singing out of tune, or that Keith Richards is playing something but not what was supposed to be there...
I know some other people having seen Madonna or Taylor Swift live and swearing that the band was terrific, when everybody is miming.
I've met people telling that Céline Dion saved the slaughter that were the Olympics thanks to her magnificent vocal technique, when it was a wonderful playback.
So, being a fan is being biased, don't you think...