With all respect to Carl, the solution is to simply write books no one would want to read. I know full well every request I get is a scam.
Trespassers William
One thing I really hate about this is that I've done at least a dozen events like this in the past that started the same way, with an email from a stranger asking me to speak to a community group. I had a great time and I think the participants did too.
With this scam so widespread, that's over.