RETURN OF LAWN MOWER ENGINE

On the 19th November my husband bought a new Magnum Petrol Engine From Rob at Magnum Motors. My husband was told by Rob that the motor would be compatible with our lawn mower that was broken. However Rob neglected to mention that the 8.5V Magnum Petrol engine that he was selling was not machined in the SA standard of millimetres but rather in inches. My husband has been very busy and had not had a chance to replace the motor until this week. He found that the motor does not in fact fit the specifications of our lawnmower and on closer inspection found the machining to be in inches. The motor has not been used or altered and is still in its original condition as when purchased, The motor was placed back into its original packaging and my husband phoned Rob to discuss the matter with him. We wish to return the motor and get a full refund, as spares will be a problem at a later date. Rob is not interested in the return, he said that the 7 day return policy has expired and offered a spare seal to compensate for his error in not advising us that the engine had been machined in inches.