First, I cannot vote because it really depends on the situation; while multiple inquiries for the same date are rare for me, every situation has worked itself out.
But here is a lesson that I learned two years ago!
Miserable old man contacts me via E-mail (in hindsight, he is a "miserable old man").
We exchange several E-mails between the hours of 7am and 8am. Naive little me is thinking, "I got this one!"
Yadda yadda yadda...being the 100% nice guy that I was, I say, "I'll reserve the date for you, but please let me know if you change your mind, so that I can open it for others," or something like that. That was my policy.
The miserable old man writes back, "Don't say NO to a customer."
I'm thinking, "Screw you, and I hope somebody else calls me now to book that date."
Nobody else called about that date, and he never called back.
Now, I am down to only 99% nice, and my policy really depends on how serious or how flakely the person I'm communicating with is.
edit: note to self: this is my post # 2 189, and I consider it the best post I have made to date.