I agree with Lady_Lust, if a client is genuine he will phone and tell you he is delayed if you hear nothing hes a TW.
BUT I have a question, what would you do if you were booked up and your (1 hour) 1pm booking arrived 15 minutes late without a phone call to tell you he was running late?
Would you.....
1. Give him the full hour knowing this is going to cause problems later by making all the other bookings after him run late?
2. Give him 45 minutes but still charge him for the hour?
3. Offer him a shorter 30 minute booking and take the loss? (if you offer these)
4. Refuse to see him?