There is another aspect of course, which is the terms and conditions of the customer towards your business and once you have taken a deposit it will be impossible to implement terms that were not already explicitly agreed before you accepted the deposit. It cuts both ways. For example, having provided a deposit, can they cancel? if they cancel, do you state you can keep a percentage of the deposit? All agreements need to made made in writing and before you accept any payment.
You change a tap in an expensive bath. They provide the tap, you charge £20 for example. You drop the tap into the bath, ruined a £1000 bath which they state you are responsible for as you caused the damage. Even with insurance, which I'm certain you all have, the insurance company will look for ways not to pay and will first refer back to the terms and conditions you both agreed upon before the work was started or payment made.