Chop and change the time repeatedly.
I recently had a reg do this, he asked to see me but didn't give a time, so I asked 9am then our usual? He says can it be 10? Okay. So on the day he asks can it be 9am actually? That's what I offered to start with! But okay, no problem. About half an hour before he was due he says actually can we push it back to 10, I've been delayed. I'm getting irritated by now, but he's usually reliable, easy and in and out within 15-20 minutes, so I bite my tongue and agree. A few minutes past 10, he texts saying I'm gonna be 15 minutes is that okay....No it fucking isn't!! It would clash with another booking and I've pissed around all morning to accommodate you already

Perfect example of when decent regulars start to go bad. Will be getting a talking to and dumped if it doesn't change.