I find that some former punters do this.    I have seen an old thread somewhere. 

They ask "I'm free between so and so today and are you free?" "I'd like to see you next Weds, can you see me?"     Even though I reply, "yes, I will be free etc etc.." and they essentially disappear (likely they have flaked off or didn't REALLY want to meet up or there was someone else/other ladies whom they ALSO asked to see etc).

I sometimes think it's a lack of respect, just playing mind games (?) or just wanking whilst messaging.  if it's one off, I'd think, "well, his job got busy" and it sounds plausible.   But a lot of TWs do use this tactic also, to get another booking, only to cancel at the last minute as "he got busy".
I hadn't blocked them if I met these men before, but now I'm considering to block them after the repeated times (2-3 times) of asking for a booking and flaking off as it gets annoying.    It does say something.  It's not the positive vibes they are sending, that's for sure. 

If i had another booking I could take then I would as I have had this happen to me.
He booked my friend then cancelled around the time he phoned me and booked me only to cancel his booking with me a hour before he was due and i had turned down others wanting to book so if you go ahead it could cost you money. We only realised this man had done this when we met for coffee and wee moaning about him then realised the name was the same and we compared phone numbers.
Your man might be different though

I think this is a very common practise with guys.  Many don't realise we talk to one another or indeed know one another.  I think they like to have back up in case one girl lets them down so that they don't go without.

At least if they cancel you are being informed. Those that don't cancel are the ones to be marked in your phone IMO.

send bill on his merry way, if we all stick together, this kind of behaviour will stop, at the end of the day we work to make money, not to be someones plan B

I'd be very hesitant to see him, I'm not interested in folk who let people down or faff around. I prefer to see those who know they want to see me, end of story.

Same, I have even had men who have told me they are booked with someone else but found my profile and would come and see me instead, absolutely no chance, its just not acceptable

I would take the booking.  Guys change their minds, that's ok.  Only way I would decline would be had he booked both for the same time, then shows clear sign of a tw.

I  would keep him in my diary but if you get anything else, I would book over him.

If he does show up, you can then explain the situation (perhaps have a saved text ready to send).

Unfortunately,  I think this happens quite a lot, we just don't get to find out about it unless it's our friend who's involved. I would still see him if you get nothing else and he turns up; why should you both lose out?

Obviously, your friend is never going to accept a booking from Bill again (I know I wouldnt) plus you both know that he is a double booker who is unreliable.

You can always meet up for dinner afterwards and use Bill's money. That's what my friend and I would do 

OR.

And this would be fun. Get your friend to come over and both be there when he turns up for an impromtu duo. I'd love to see the look on his face.  That's the kind of thing my friend and I do.