That's actually exactly how it works in South Africa. Every parking lot have multiple "parking attendants". They're not paid for by the lot owner, they work on tips and each person guards a couple of rows of cars from breakins and thefts. Nobody is armed, it's just big intimidating guys walking around the lot. It's a gig economy that popped up by itself in the late 90s.
And it really works, even though South Africa has one of the highest crime rates in the world, parking lot breakins are very rare. I had no qualms about leaving a Mercedes with a laptop in it in an open parking lot.
Before there were parking lot attendants - circa 1995, I had my car broken into and speakers stolen, in the parking lot of a police station. Go figure.