this should be looked into and specifically written into the contract by the booking agent, producer or venue owner....perhaps the person
puttng on the concert was jsut as surprised as the audience members (those who paid any attention ) and they might want it planned in the
future...and tell the performer that LIVE music means "live" music.

I have heard some musicians who otherwise play good acoustic music
get so involved in the effects that it does not seem live anymore.

so, it is a good rule: if you want to "play with yourself",
do it in private!

some musicians also send around a demo disc, to promote their live
performance, that includes all sorts of studio musicians who will
not be with them when they arrive at your venue on their tour.

false advertising!