Heston,
With an attitude such as portrayed in this thread - how are you still in business?Do you manage to survive on a bunch of 'old boys' who did their PPL back when you first opened the school, to take an occasional flight with an instructor for renewal / an occasional local trip? Surely that type of attitude cannot possibly get you any new business!
It doesn't take long to be nice to them, explain to them how it works, and get them booked in for a trial flight! Convert prospect to business in order to convert a failing to a prosperous business. A whole 10minutes and you've got yourself a potential recurrent customer who will spend £10k+ with you over the next year!
Again - in your garage, why do you need to delay the works on the paying customer's car? It only takes a few minutes and you don't get many new customers through the door!
I agree with Capt Kremmen on this.