If someone says they have a "policy" of being paid in advance, I simply respond that that is a dealbreaker for me and ask if that’s a "dealbreaker" for them. If they say "yes", then I thank them for their time and I move on. I’d say about 50% say it’s a dealbreaker for them and about 50% agree to meet without being paid upfront. If they do decide to "break their policy" for me, then I make sure the money is clearly visible when they come into the room. That seems to be enough to set the skeptics at ease. I’ve had some great times with some guys who have broken their policy for me, so I think it’s worth at least asking.
I will tell you that refusing to pay an upfront will piss some guys off. I’ve certainly been spoken down to, berated, and even threatened for refusing to pay ahead of time. The funny thing is, the more agitated a guy gets, the more I think he’s a scammer, and the more I think I just dodged a bullet. So it’s a win-win in my book.