In the years when I ran a club I don't think that this was ever an issue. If the performer arrived with spouse or a driver then they got in.

When I became involved with larger venues people putting up the guest got freebies otherwise it would be 2 guests per person max. The guest list is ALWAYS agreed before the gig, if your name isn't on the door then you pay. (There may be a refund when an apoligetic band member comes round in the interval but that is another matter)