Customer Issues

What a headache, I Run a motorcycle repair shop and a customer dropped off a machine to be diagnosed. I diagnosed the machine, they decided to do the work themselves, they owe for the diag only. Its been 3 weeks and they wont come pick up the machine. Turns out the son has power of attorney of the machine which is his dying mother's.. the step dad brought the machine to me but fully ghosted us. The son wants to pay me to trailer the machine back to the step dads home and get the bill settled. What the heck am I to do. This is a professional shop and everything needs to be legal. I dont like the idea of dumping the machine on someone's property without consent from that person aka the one who ghosted us. Any advice as to how to deal with the situation would be great! Thank you.