How to successfully purchase companies with operator in place?

I know this is a cliche question in the ETA space and that you should first work in a business of any substantial size before hiring an operator. However, I am looking for ways that people have successfully ramped into the ETA space and built a healthy cash flow before quitting their W2 job (or keeping their W2 job). I am mainly looking for ideas of how others have been successful doing this (outside of acquiring little stuff like ATM routes, vending machines, etc.) Thanks.