I also vote 'no', but would add that there are sometimes real reasons why people have to cancel at the last minute. Whilst we would always get in contact to explain the situation, even after that people have accused us of time wasting. Here's some real reasons we have had to cancel at the very last minute (grrr):
- Child sent home from school for being naughty;
- Cat being bitten by a fox
- Flood (burst water pipe)
- The curse (we don't have that happen to us any more thankfully)
So you could find legit people being cast as time wasters. Validations are a much better system imho