"That's the way we really are" joke

I heard this joke from a friend two days ago. It is an ethnic joke,
but I am Sefardim myself and we don't take ourselves all that
seriously.
Moshe Kohn opens a Kosher restaurant in London and puts a notice in
the window "ARABS NOT WELCOME"; a couple of days later, a person of
obviously Arab origin walks in and requests a sandwich - so the
cashier quickly runs into Moshe's office asking what to do. Moshe
decides that he really doesn't want a scandal, so he orders "OK, give
him the sandwich, but charge him double - that should teach him."
No sooner said than done.
But the next day the same Arab is back again - this time for a full
lunch; Moshe decides "Charge him triple, he'll get the lesson this
time!" The Arab eats his lunch, pays without a quibble, praises the
food and even asks for a reservation for 10 of his friends for the
same evening. Moshe decides "OK, let him have the reservation, but if
his friend do come, charge them tenfold!" The Arabs appear in the
evening, have a large dinner, pay without complaining and even tip
generously. So the next day Moshe puts a new sign in the window:
"JEWS NOT WELCOME."