Thanks again for all the comments. As a newbie, and apologise if this is stating the obvious, but I was always under the impression that there were two fundamental ways of specc'ing out a job e.g. an 'estimate' or a 'quote'. A quote is a fixed price. If the job is done quicker, you still pay the same price. If the job goes over, you still pay the same price. However, an 'estimate' to me means that when the job is completed, the contractor performs a reconciliation and invoices the actual costs. If the job has come in under estimate, the OP gets the difference back. If the job took longer, the OP would be expected to pay any extra cost. In this scenario, there is also an obligation for the contractor to let the OP know that the job is likely to be coming in over budget before the job is completed.