I don't even ask the indy shop I use how they are fixing the flats/leakers I bring them....I see all kinds of commercial trucks, construction equipment, tractors, etc. getting their tires serviced there and figure that those people need those vehicles to work to make money and would be unlikely to use a place that doesn't get the job done. If I bring them a tire on a wheel when they aren't super busy (like in winter tire on/off weeks), they will have the patch/plug job done in half an hour.
Assuming I have to use them for that kind of job again, I will ask about what kind of repair they did just to satisfy my own curiosity. Just brought them a snow tire this past spring that needed to be topped off every week or so during the winter, I couldn't see anything wrong with it but they told me it had picked up a screw.