If there is a dispute about the standard of service, fine, it must be sorted out first but, there are plenty of people who want the work done but delay payment for as long as possible or just refuse to pay. How bad can your workmanship be when replacing a socket outlet? If my materials exceed 1K I will ask for the materials cost up front but, when the total is less then 1K, I go ahead and do it. This has earned me a reputation amongst honest clients that I wish to keep. I do not mind waiting a week but 6 months? A year?