Rope...and lot's of it

Seriously tho (albeit that is one way to make sure they don't flake out on you...assuming they are already there), you could improve your screening to qualify each subbie.  You might want to see if they have played in that world, and if so get a couple of referrals on them of Domme's they have already seen.

If they are newbies as well, you might want to see some way of verifying that they are really into the scene.  And that may include better communication (either emails or phone conversations) prior to the session.

Good luck to you.

make it a two-part type screening. Insist that they answer certain questions in an email besides the usual screening of name and phone (Have you been a sub before and for whom? How long have you been playing? etc.). Then if they answer the way you want them to, and you think they might be serious sub material, insist they meet with you somewhere for coffee so that you can get a better feel for them and can find out more of who they are.

D/s is not a game for amateur subs - and too many men will not understand what you want them to do unless a) they've already been subs before or b) if newbies they have at least some understanding of the situation.

Also, this is a good question for the BDSM board (it's new).

If you can find a mentor or discuss on the Provider Only board.   I'm not into this area personally but I know of others who have their own dungeon.  I don't think that's wrong at all.  One lady gave me a tour of her incall which included such an area.   I think you got good advise.  In order to give a good experience (defined as what the client wants) you need to know what that is, how experienced they are, etc.  So I'd think some discussion of that would be in order.   You'll probably want to increase from what you ask now & tweak it as you go along.
Best wishes,
skb