Sorry but I don't prescribe to this opinion, I have loads of numbers stored that are, what I call, serial timewasters. The majority of timewasters are small, minded individuals who get their kicks out of wasting our time. Usual story of, the minority ruining the fun for the majority.
Get the guys to confirm an hour or half an hour before hand. Keep every number that wastes your time, they will try the same trick again.
Sandy x