If they're a true witch, they won't tell you. Real witches don't have green skin, they're not evil, they don't dress weird, and they usually don't have warts. Witches will be connected to nature, but that's the only hint that they'll normally give.
Well, usually the broom is a dead give away, even if they don't fly it any more, they keep it for sentimental reasons, as the cauldron and a couple of other things. But the one thing that will tell you EVERY time, is that they float. So throw them on water, if they float, they are/were a witch.
wow... So many posts that are just mean. Witchcraft and Wicca are legally recognized religions. It doesn't matter if you don't believe in it. Someone else does. I call myself a witch. I worship a God and Goddess. We're all different though. And no that does not mean you can cast a spell on someone to turn them into a frog. Why would you want to do that anyway?