Selling goods to gay people isn't breaking any laws in the bible, and on a legal note, it is not a business owner's place to dictate a customer's private life, nor is what a person decides to do with the produce sold by a business - except in the case of weapons, cigarettes, alcohol or other controlled or dangerous items - ultimately any of the seller's concern. A shop owner who thinks they wield any power to refuse law-abiding citizens because of the personal choices of their private lives is delusionally self important.
The shop owner's attitude is one of much ado about nothing, and since in the eyes of the law, marriage is a legal agreement, not a religious one, and since business is a legislated practice, not a religious one, and since neither gay marriage nor cross-dressing are illegal in the relevant places, the shop owners are on thin ice, legally.
There is also absolutely no evidence to suggest refusing service to gay people will in any way influence their decision to get married or not, nor is there any tangible biblical precedent for refusing someone service. There is also the biblical saying, 'a person cannot serve both money and God', and since money, like business, is a legislated concept wherein certain laws apply, a person cannot harmoniously be bound by the legal obligations of business and simultaneously work to enforce their religious beliefs on customers. It is a conflict of interest to be bound by secular business legislation and simultaneously apply values that lie in breach of many of the business obligations to which one is bound.
One of those obligations is non-discriminatory service and overall acceptance of the legal precedents of business ownership itself.