What if the customer isn't a person?
If it's not a person what the hell is it? For the record, I'll take anybody's (anything's?) money, also under the Washington State ADA you have to allow service animals in your establishment.
If you're trying to be coy about a religion being the customer, in the United States a corporation (which an organized religion is) is a legally the same as a person. See Citizens United v FEC. Which I think was probably legally correct but morally wrong. While we're at it, I think the Hobby Lobby decision was wrong. If I was CEO of Michael's (HL's main competition around here) I'd sue the Feds and demand equal treatment under the 14th Amendment.