Okay, one person in a workshop. Do they:
a: do three puncture repairs for £7.50 (say) in an hour, minus costs, making about £15.
b: do one full service, making about £50.
The only reason to charge less for repairs is if you’re sitting around twiddling your thumbs. Puncture repairs might be quick to do, but they’re also spur-of-the-moment, people often turn up and want them done there and then, meaning you have to drop what you’re doing, find a spare workstand, etc.
This is a silly argument, though.