It's a lot of fun. You get a lot of no answers this early in the cycle. Usually, though, you're speaking to people who already lean towards Hillary. People aren't usually that rude. Worst thing I've ever gotten is people who say "I'm voting for her, leave me alone." I've never been cussed out or yelled at or anything too bad.
The numbers are from known/likely supporters, usually. Give it a shot. It can help a lot, and if you hate it, you don't have to do it again. You can find other ways to help.
So registered Ds at the very least, then? That's comforting, because I live in one of the most Appalachian, virulently pro-Trump areas of the state. I guess I'll try it once and see if it's for me since there's essentially no Democratic party apparatus elsewhere in the county. Thanks!