Some years ago I had a customer for about a year whose elderly father was still an active part of the day to day business. He had extremely poor sight, so bad that he could only read if he held everything almost touching his nose, this even while wearing his milk bottles.
I had problems with this customer since it was never clear who was in charge, son or father. Whichever they always provided the parts they wanted fitted new or secondhand. I was only ever asked to do repairs which they didn’t feel like doing themselves. Quite often whatever I said required doing would be challenged particularly if either one of them thought up what they thought might be cheaper. Whenever I was working for them son would normally disappear delivering for most of the day leaving father in the office.
Three times the same thing happened, father put ATF in the clutch fluid reservoir with predictable results a few weeks later. The final straw came when a Scania clutch servo had to be renewed and they started blaming me.