Couldn't resist passing on this story from
Usenet/rec.music.makers.piano:-

Dan Wilson, London

 - - -

Roy, I've had that happen myself. It just hasn't sunk in with some
people that they have no hearing over a certain frequency.

I had one lady who kept insisting I was "tuning it wrong" even though
it was fine.  On my questioning, she admitted to being having serious
hearing problems (hell, she could hardly hear me talk), but she didn't
see why that should affect how she hears the tuning.  I left with both
of us exasperated with the other.  They (her and husband) came in the
store later and I overheard them complain to the owner that I did a
bad job.  I told the owner I wasn't going back there so he gave the
assignment to another tuner to just tune it to whatever she wants.

I talked to this tuner later and asked him what happened and he said
that they agreed that she would just "tell him when the note was
right".  What wound up happening was that my tuning was fine with her
until the treble break, at which point she started dictating to him
what the note "should" be, and in order to please her, he ended up
tuning each successive higher note to be *lower* in pitch than the one
preceding.  In other words, as you played *up* the scale, the pitches
went *down*.

It's a good thing I didn't go.  I may have blown my stack.

Rick Clark