Mark the glazier, state of the art window manufacturer and salesman had to call a customer for non payment of her account.
"Excuse me Mrs Halliday" Mark began "It's Mark here from Crystal Clear Glaziers. It's about your account for the windows we fitted last year. According to our records you still haven't paid for them yet?"
"But dear.." said Mrs Halliday "when you sold me them you told me they would pay for themselves within 12 months!"