I think redd_foxx may have the right solution for this, as per this email from her:
I would be volcanically angry if that happened and around twelve phoned his office for a progress report as they must be able to contact these guys. I would think they call in when completing jobs so they are trackable. When one does arrive you have my permisso to open the door, say"BT Man?" and he confirms, whack him right between the eyes.No apologising and helping him up, offering a tissue for the nose bleed or anything, if he attempts to speak, just knock him straight down again. This method of approach establishes customer superiority and does away with the usual rubbish of them thinking you have any interest in them whatsoever.If he cant just quietly enter, go about his business efficiently and leave, phone his office while he is there and say you're furious that he hasn't turned up and that his van is parked at a rakish angle on the pavement outside the local pub. That'll show him. Sorted. You'll have him eating out of your hand if you just show him who's boss. The customer is, after all always right .