Never accept cash without a record

Especially when you're working with friends or relatives. I had this bad experience with a relative who insists that he paid me cash for a contractor's invoice. Funny thing was there was no record of any sort except the fact that there was an invoice and a call from the contractor demanding payment. Excuse me but I do have some confidence and personal principle when it comes to money. End of the matter was that the relative agreed to pay reluctantly but then again that left a lot of bad blood abrewing because he still thinks he's right and so do I. So if you ever chance to come across such incidents, do not ever accept cash without a record. Of course there were times as well when the customer insisted that he paid cash for my services...