People often have mechanical problems with their vehicles and instead of trying to fix it they buy a new car. You can sometimes get them to sell the car for half the value, especially if it's not running.
I bought an SUV for $1000 because it wasn't running. I spent 4 hours and $300 replacement a sensor and the brakes on it. I then sold it for $3000. That works out to $1700 of profit for 6 hours' work if you include the time to sell it. That works out to $283/hr.
They don't always go as well as that one but it's usually pretty close
I tend to browse FB marketplace when I'm bored and look for cars that are listed for less than they seem to be worth. I don't really actively look for them so it's usually a few months between cars because I'm busy with my real job