I want to report it because...
It is not right.
If I see some football player being robbed by someone in front of me, I'd call a police or give him a help. I can not say that "oh, he is big. he can take care of himself" or "he is rich. it is ok if he lose little money".
This is how "I" deal with these issues and if I see a fake watch being sold, it is wrong in my moral standard and I feel I am obligated to report this problem to a right person.
again, this is how "I" feel and am not telling anybody to do the same as I am sure everybody feels differently and have different standards.