interview. Usually, I send it to them a few days ahead of time and
explain why we need it and to feel free to call me if they have any
questions or concerns. I ask them to bring it to the interview.
I've never had anyone question it (but I did have a "willing expert"
become "unwilling" when presented with the release AFTER the
interview; it was a big blow to both of us for feeling we had wasted
the time of the interview).
With "man on the street," I judge the circumstances of the
interview. In general, I also try to get the release signed before
the interview, but have done it after as well. I usually find that
using a dose of humor helps - "Now's when I need to ask you to sign
your life away," followed by a brief explanation of why I need the
release (similar to what Doug said) usually does the trick.