"How dare you bring your Satanic devil cards in here? God will rain down his displeasure on you!"
"Ma'am - if you think I'm such a scary witch, maybe you should be running away from me right now."
That was a fun day. I was doing readings at my friend's booth at a flea market, and in walked this woman. She watched me read for a while, walked up and talked about God raining down displeasure, etc. After I told her to beat it, she did. Then she came back with friends and pamphlets about Jesus and tossed them down on top of me. That went poorly for her and her friends.
Although I wanted to get into a debate with her about who was right, what I ended up doing was calling security and getting her ejected from the grounds. It wasn't because I was afraid of her, and it wasn't because I was intimidated. I didn't debate her because it's not my job to educate ignorant people.
It's kind of like arguing about politics on facebook. It's a waste of time. If you're old enough to have a facebook account, your politics are likely concrete, and there is no good way to have a debate with another person about something that you're both holding inflexible opinions about. It's a waste of time.
You are going to encounter ignorant folks when you do readings. How you deal with them is obviously up to you, but I want you to remember that you don't have to teach them anything. You don't have to listen to them. You don't have to be nice. You don't even have to be respectful if they're disrespecting you. What is that line I saw? You're not the jackass whisperer. Just see them out and walk along.
It's not your job to educate folks.