It's pretty common knowledge that "performers": Britney, Madonna, etc lip sync most if not all their live stuff because of the demands of dancing and singing simultaneously. It's not my bag baby but I know the deal and so it wouldn't bother me if I chose to partake.

Now if you're talking about a real band, actual musicians, I would 100% expect a true live performance. Backing tracks are OK as long as the main vocals are live unless there were some extenuating circumstances. Anything else is cheating the audience in my opinion.

Has happened twice to me that I know of.

First time was seeing Kansas in their heyday. ('77 or '78) The band was "playing" and one by one they set their instruments down and walked off stage waving to the crowd while the song kept going...and the crowd was cheering!
I WAS FUCKING PISSED! I paid this much to listen to someone's stereo?
(granted, it was a really nice stereo but still, so was mine at home)

The second time was seeing ZZ Top at what is now Comerica Theatre. The LAST show I ever would see them play.
(sad too because I would travel to see the The Reverend Billy G play)
Great show until they started to play their anthem, La Grange.
One of the guitars synched tracks *wasn't*. It was a beat slow, so the song sounded like some kids in a really shiity garage band who never played together before. First time I ever left in the first third of hearing that song live.
What a shame. Play or freaking retire, either/or, make up your mind.

35.7% of the ticket cost should be refunded

I would feel cheated if I went to see a musician perform and got lip sync instead. I guess we should be used to being fooled and cheated. Been going on longer than you think.

Remember the TV show “Mr, Ed” about the horse that talked? That wasn’t really the horse talking. It was lip sync. See, they’ve been cheating us for a long time.

My best buddy has seen ZZ top a dozen times, since High school.

he told me that he thought that they had started lip synching, I told him that he was nuts, they would never do that!

will have to apoligize