Further to the information that you gave to the Mazda owner last week, I would like to add the following in your defence. The owner did not state what mileage he had covered. Generally, engines tend to "loosen up" after about 6,000 miles or so thus improving mpg attained. Motor manufacturers are governed by very strict guidelines as to how they obtain their mpg figures and for this reason, all tests are (or at least used to be) carried out on a rolling road. This, as we all know, bears no real resemblance to day to day motoring. Driving style, road conditions play a major role in this aspect, never mind the state of the vehicle itself, tyre pressures etc. Your reader would be best to ask the dealer to carry out a controlled mpg test. This involves the dealer witnessing you brimming the tank, you doing an agreed mileage and then bringing the car back with the dealer again, witnessing the car being filled back up. It is then down to simple mathematics.