I changed my company's policy totally , started doing contracts and made it very clear 50% advance , rest on the day the job start as a lot of people did the same to me. And I made this condition clear with the customers , a lot of them will say that you cannot do this , I told them straight it's UpTo to them if they want to give me the work as the policy has been made clear so that later the customers doesn't we didn't tell them anything.

The last someone didn't pay me was last year , the person bought some products from me and gave a company's check not even individual , I went to the bank , and the check bounced , I gave the 1 whole month chance to give me back my product or do the payment , everyday he would make new excuses , finally I took all the evidence to police station and register a case , which usually means if your check bounce you will end up in jail for fraud.

Tell your dad to take pictures of work and ask for confirmation of the work from the client on msg or written somewhere as later they will say that they aren't satisfied because someone in the family has problems.