Welcome to the forums.
Last week I bought a car from your garage, with the assistance of a most helpful member of your staff.
However, a week later the engine ceased working and I returned the car for repair. I was shocked when I was told that the repair would cost me £400! The car only cost £700, and as there is a six-month warranty I should not be expected to pay for this repair.
As the car was clearly not fit for use when sold, I require full reimbursement.