I don't really consider this as a form of good money making at all.
Enforcers can only return vehicles that were stolen. You assume that there will be tons of stolen cars, which there really isn't due to people preferring to use their own vehicles. Not saying there isn't any at all, but you can sometimes spend over 30 minutes just trying to find a single stolen car. Not to mention, not all stolen vehicles will reward you the same money. The type of vehicle is considered, making sure the car is fully repaired for pristine bonus. Also considering prestige which goes up much slower than notoriety.
And then you're kind of forced to use a starter car, because the amount of times you have to summon back your own custom vehicle (costs $100 per summon) to get back to stolen vehicle hunting, can really just take away all the money you earn from just trying to return stolen cars, so in fact, you could lose money.
This is coming from someone who has done a lot of car returning for TONS of hours.
I never said that criminals can't attack enforcers that have money. I welcome it.