You can do well detailing if that's what you're set up to do. As a sideline to carpet cleaning it would be a pain unless you really loved doing it.
Pricing from a well regarded local detailer. (Always busy) They sell lots of add-ons as well as exterior detailing. They say the average job ticket is around $400.
INTERIOR
Vac + Wipe,
Steam Clean Panels + Seats,
Deep Clean Carpets + lightly Clean Headliner
Condition leather seats
SM $200 | M $225 | L $250 | XL $275
Another detailer about two miles from this one does not advertise, has no web presence, and is booked out three to four weeks. His interior detail starts at $400. He wouldn't say what he averages.
PS: One of our ex-employees started a detail shop and was doing great until he morphed out of the business. He did a few specialty cars for dealers and they liked his before and after photos so much they paid him to take pics of their cars for ads. That's all he does now - or I guess did, since dealers aren't selling much these days.