".....If they did a good job, they could use photos for next year's sales proof...."

If I were a custom drone application business, which I'm not, I'd be checking on myself now. I don't care who the person/business is, but everyone has screw-ups sometimes. Maybe they knew about it at the time, maybe they didn't. But hopefully they have some good resulting fields also. Either way, I would NOT publicize the problems if it were attributable to me. I would take those problems and analyze them. Too fast? Too high? Too wide of swath? Wrong product? Defective machinery? Improper mixing? Take photos and analyze them. If applicators don't go back, how would they know? Try & fix the problems next year.

When we work in our own fields, we see the results usually in the fall. If any problems, they probably show up. Blocked nozzle, ran over a row, etc, etc. How can the custom applicator check himself? Aerial photos.
However, I would save the good looking fields & use them for ad purposes. What business in the universe advertises it's mistakes?

I think we all know that if a custom applicator claims to have 0 screw-ups, they are not being honest.