Ya I think it is SO unfair, wrong, unthoughtful, mean, selfish, stupid and does ultimately have a negative affect on other Punters!
I know that I myself have had to cancel my appointments (normally due to work commitments) but on each occasion I endeavor to do my very best to give the Escort as much Notice as humanly possibly along with my most sincere apologies.
One suggestion I would have, would be to save this "Clients" number on your phone under "DO NOT ANSWER" and if/when he calls again you simply ignore the call. I guess anyone should be given a 2nd chance, no-one is faultless and circumstances can pop-up where by the Booking cannot be carried out as wished.
I'm pretty sure that Escorts (a lot of the Independent ones anyway) do exchange information and chat to each-other from time-to-time. Maybe they could share info about "No-Show" Clients in various areas or towns and help each-other to prevent waisting their time even taking calls from these wasters?