How many times should a merchant be allowed to repair a product that malfunctions before he has to provide a replacement?

Under the Sale of Goods Act a merchant must provide a refund, or a replacement when it is clear that the item cannot be repaired. However, the number of times allowed for repairs before the item should be replaced is determined on a case by case basis. It may be possible that the merchant might have missed the real problem in attempting to repair the item on previous attempts, but shows proof that he will be able to make the necessary repairs to the satisfaction of the customer, if a further opportunity to do so is allowed. Whether or not the merchant would be allowed to make that attempt is based on the facts of each case.