I agree, when somebody employs you, accurate arrival times should be of the essence. Furthermore, if these times cannot be met the client must be informed in advance as much as possible. These are essential traits for any businessman.
But, how often do tradesmen call at appointed times only to be informed:- "Now is not convenient, sorry . . ." This happens too and is costly to the tradesman.
I'm not offering this as an excuse but instances are fairly common. Also, it is difficult to receive payment after the job is finished "My husband will send you the cheque . . ." Then you receive the phone call "How much less do you want to be paid?" "Quantify your charges" - wait for it . . . "What's your PPS number?" or the classic "You'll be paid at the end of next month, just like all my bills."
My advice (for all its worth) is that when a job is completed properly, pay the agreed price. Get your receipt. If the tradesman was good employ him/her again. If the tradesman did a 'half-effort' then dont pay and dont re-employ.