But it does get into the "prove you're you" problem when people demand photo ID for a use name that is not the same as that on your legal ID -- which I've encountered when paying on the door, not just as security on pickup of pre-reg.

Believe it or not, given my desire for people to have a name on their badge by which they are known within the community and to which they will answer, I'm sympathetic with you. I don't know why someone should need to provide photo ID for a membership purchased on the door for cash. I've never heard a convention provide a reasonable justification for doing so. I've concluded that we have a lot of people for whom Your Papers Please is a Way Of Life.