I got trolled so hard, so many times while working in the 'goth' store. It just draws the religious crazies like flies. What's worse is that when they couldn't get anywhere with me they'd start preaching to my customers instead. Sometimes they would come in and hide bible tracts all over the store. Other times they would hover outside and try to convert people as they walked in or out.
On those occasions I could just call security and have them handle it. But when they were in the store the situation was trickier. Obviously if they were talking to me or my staff, I could deal with it, and I did so very well.
I found complimenting them worked wonders: "Faith is such a beautiful thing to have. I can see how fulfilled and happy yours has made you and it's so wonderful that you have taken the time to share that with me today. It's a rare thing to find generous people in this world...." etc.
They would be so floored at my compliments that most of the time they would forget that I never answered the question.
The big problem was when they approached the customers. I couldn't just say 'don't bother them' because that would offend them and cause even more problems. "We're just people having a conversation, are you saying that people can't talk in your store?"
So I'd have to try and get the customer isolated by asking them a question on merchandise they 'seemed interested in.' Other than that, there wasn't a lot I could do if the religious person was being somewhat nice about it.