I agree it's a lot of wear and tear on the car, but if it's a good payoff,and makes a profit in spite of that depreciation, it seems good. But the important questions are:
how much time does it take set up the shop, to do the on site part,then the report?
How much does that produce per hour of your time?
Is that what you think your time is worth?
Depending on that answer you can tell whether it's a for-profit activity or a pastime, for the fun of it. And you'll be able to tell if your husband is being "very negative," or is he evaluating the results correctly.