Mr and Mrs Carter decide to install double-glazing in their house. They get three firms to provide 'estimates' for the job, the cheapest (£4,000) being submitted by Kozee Ltd, which they ask to do the work. The Carters sign a contract, but the document does not mention the price payable for the work or how long it will take to complete. The workmen start the job in July, but the work proceeds in fits and starts and is finished finally in December. The Carters are very unhappy with the workmanship; the house is still very draughty and there has been no noticeable saving in their fuel bills. They have now received a bill from Kozee Ltd for £9,000 and they seek your advice.