I had to deal with a few skeptics. They list all these things about "how" something is done, ask about credentials, and really put you on the spot about everything. There's so many questions. Usually they'll ask something that they could easily judge if it's right or wrong, like an anniversary or a birthday. I just tell them that it's not great for specific dates, but it can tell you the situation of what happened on that date, because it works more like a storybook, rather than a calendar.
Surprisingly, I thought I'd get lots of negativity from the Christian folks about the scary Devil in the deck. Usually they'll ask about it, and I'll just tell them the meaning of that card (control, manipulation, overworking, deprived of something, lust, etc.), then I tell them that it's just an image on a piece of paper. The only harm it can do is probably give you a paper cut. It can't be as bad as the actual people or situation it's trying to represent, or warn you about, right? It's just a flat piece of paper. There are people who are cruel to others, and this card just tries to represent that.
And then for those skeptics trying to prove me wrong in every shape and form, I just tell them that if I'm doing anything suspicious, just let me know. I also tell them that I don't really know if all of this card reading stuff is real or not, so if they want to show me that it's not, then please do, because I don't want to be going around tricking others with it, since all I want to do is help people with it, not to trick them with it!
Then while I'm reading, they're watching me like a hawk, ready to disapprove any suspicious moves I make. But I'm not set on proving them wrong. I just want them to judge it for themselves, just as I have for myself. This kind of thinking keeps me calm and friendly towards them.
I usually read for groups of friends and acquaintances, and even though there are some skeptics, I just tell them to have fun with it, and see where it goes. In the end, they're usually happy with the reading, and say that they believe in me, but will still go on and on about how "other" readers might be tricking people! Bleh, I guess they will have their opinions, but at least they've opened up to the idea about readers a little bit, right?
There's better to leave things incomprehensible. I was also answering questions and at some point couldn't find any answer. When I do bigger readings with few spreads, first one is for general feelings, second for more details - sometimes they can be far away with the meaning but all the feel from first spread is still in there, to not mention the same cards or ones with similiar messages. And of course the core of the first little reading is helping with all the rest. I don't know to explain it and I know only one person who like answer like that.