That only makes sense if you have the opportunity to make more money than you'd be paying the mechanic with the time you spent fixing the car. I'd venture to say that's true less often than not. Even if you day job makes more per hour than you're saving by repairing the car, it doesn't necessarily mean you can just choose to book more hours on the job. To make it more concrete, let's use the given example. Let's say the repair is $300 in parts, and $700 in labor. Let's call the shop rate $100/hour, to be conservative. So in order for it to make sense for me financially, I have to a) have a job that makes at least $100/hour and b) have the choice to work an extra 7 hours.