Also, probability of going into seriously heated argument is constant for each sale, and is a factor of a buyer (of a shop too, but we're only looking at one sh

Also, probability of going into seriously heated argument is constant for each sale, and is a factor of a buyer (of a shop too, but we're only looking at one shop, so it's a constant). So, if this already has not hapenned enough times for a customer to become a regular, we can conclude that there's very low probability of this happening ever - i.e. people who become regulars do it because they're satisfied with the service, and it will probably stay that way.