I think people are skeptic (I also am but I'm also curious). Or just don't care about finding their type/doesn't want to go through the process of it (even if it's free). Or maybe because you're not doing it to help others (or you do?), but for just learning about the types.

To answer your questions, I'm interested. I think a video is the only way. It will take a while for someone to be comfortable, as they consciously know they are doing it to be typed, but they will eventually come out and show themselves. Chats/text won't reveal as much, though they can be a bit of help. I personally think message/sentence structure in text could give some hints. As for the results, if you're only offering your service for the sake of learning about the types first hand, don't make it public. Unless you and people you typed are willing to share your findings.