Firstly I will say that in their defence Napp Rental Insurance is a legit company. I am registered with them as my guarentor company for my rental property in Osaka prefecture. The staff are very polite on the phone and at first were simply calling to confirm my details (although there was no real reason they should have to do this as my letting agent would have confirmed this all already.
However after that they were trying to sell us a water dispenser service. We politely declined and told them if we changed our mind we'd be back in touch if we didn't want it we wouldn't call again. Nonetheless today they tried calling again seemingly to try selling me the service again. It's pushy and it gives the otherwise legit company scammy vibes, which I don't like when we should be able to trust them as an important service protecting rental payments. When I move to a different address I will ask that my letting agent uses a different company because I really don't like the way they run the their water dispenser campaign with their desperate and persistent sales attempts by phone.