Even tho' this was 15 or more years ago I still remember a customer who was a nightmare to deal with.
She was an elderly lady (80 if she was a day).
Upon arriving at her house, she told me that she'd turned to me on the highest recommendation, because none of the previous tuners she had tried were able to tune her (nearly new) piano to the standard she required..... and that they were "unreliable", because "when I've phoned them to ask them to come back and correct their faults", they promised to return her calls & never did.
It wasn't long before I added myself to that list!!!
I did perfectly good tuning for her and, like Jerry, not only played the piano for several minutes so she could check it - but had her play it too.
She said she was delighted - "it's never sounded so good".
A day or two later & she was on the phone.
"There's something not quite right with 'one note' the piano".
I went back to check. The tuning was still perfect.
I tried to explain to her (by demonstrating all the various checks) that there was nothing wrong, but she insisted that E5 was "terribly flat".
I asked why she hadn't voiced her concerns at the time.
"It must have gone out of tune since you left".
Although the note WAS perfectly in tune, I agreed to tune it to her liking.
When she was finally 'happy' with it, it was WILDLY sharp. I said I wasn't happy to leave it like that, as it was my name that was associated to the tuning..... but she insisted, so I reluctantly agreed to leave it as it was.
Another day or two passed..... & yes, she was on the phone again - the note still wasn't 'right'.
I said to her that I'd tuned it exactly how she wanted it, but (as she was only about a mile away from where I lived), I called round again.
This time I put it back into perfect tuning again - and she was, once more, delighted.
One or two days later - (you guessed it.....)
This time I was 'too busy with other work' - and thankfully never heard from, or saw her again!
Some people, eh?