A:
Well all I can say is that we have been using them in our church where I am maintenance coordinator for many years now with no issue. Have 2 of the NV501's that are over 5 years old and used to clean about 20,000 square feet of carpet area weekly. Just had to replace one as it would not power on but, this was due to a volunteer running over a wet area in the carpet and sucking up some water into the unit. Repair would have been half the cost of vacuum so just replaced it. Wife has an NV501 and NV750 that she uses in house cleaning service and has never had issue with them.
Now with that said, I believe Shark will not warranty the vacuum if aware it is used for commercial purposes. However considering the ones we have would be out of warranty by now anyway and the use and performance my experience has been with them, that is not an issue for me.