I can think of any number of ways of making the deviants, in the end, wish they'd hired somebody else.
I've always believed these types of businesses should avoid the legal hassle and dodge the question:
"Yes, of course I would be willing to film your ceremony; that will be $58,331 for up to two hours of video and 30 minutes of editing." Or,
"I am not legally permitted to refuse, so I won't, but I would be extremely uncomfortable at such an event and would recommend you hire someone who can better capture the true spirit of the celebration for you." Or,
"Yes, that would be fine," until a last minute cancellation for personal/health reasons.
Any thug who insists on another person's unwilling acquiescence deserves whatever offense or disappointment results. Given the weaponized use of big government to harm ordinary people, even the most truthful among us have no moral obligation to deal with gays demanding services in good faith.
The trick is to be subtle. No outright sabotage, just mediocrity. And be sure to cough and blow your nose during the entire shoot because you have a cold.