Christmas "overtime" premium?

[David Renaud]

Lets say your booked up too capacity and then some till Christmas.
What is the consensus about charging a premium for short notice
"emergency" tunings.

For example:     Last week someone requests four
concert tunings on 24 hrs notice. There are two grands to
tune together twice for 4 hands concerts.  They are coming
into town after sitting in a cold truck for a few days.
They want them both done on the Friday and Saturday.
Yes, they waited till Thursday to book a technician.
I already have over 12hrs work both days, but it is possible
and 5 min. from home. The usual people I call for help are busy.
The client was insistent that they should get a discount for the
second piano as usual, but I was insistent that I
should not be doing it, but if they must have me I would charge
my regular rate for each, no discounts.
They reluctantly paid, but not without some tension.
Worked out OK. Pianos were very nice. Easy tunings.

So.
In general is it wrong to charge extra for emergency overtime?
Would most people walk away, avoiding creating ill will with an extra
charge?
How do you deal with promoters that order tunings like ordering pizza.
I've heard of a technician charging $250 to go out on New Years Eve on a
couple hours notice.

                                All opinions welcome
                                Cheers
                                Dave Renaud
                                RPT
                                Canada