[Avodah] Business with an Akum

[Alexander Seinfeld]

One is not permitted to do any kind of business with an Akum
(idol-worshipper) on the day of their festival (nor 3 days prior in the
Land of Israel) - Rambam Hil. Avodah Zara Ch. 9, Shulchan Aruch Yoreh Deah
148.1.

Question - Today, if I know a shop owner is a religious Xian, am I allowed
to shop there on Sunday? Or if I know he is a religious Hindu, do I need
to mark my calendar with all of the Hindu festivals and avoid his shop on
those days? What about a traditional Chinese person on Chinese New Year?
Or a Catholic on All Souls Day? If so, is there any halachic literature
that lists all of the dates currently forbidden?

(I¹m also not allowed to sell to him on his holidays, and if I do (in
error), I¹m not allowed to enjoy the profits of that sale.)

Alexander Seinfeld