I did say this is when they have already been round. I wouldn't expect them to turn up and just magic stuff out of thin air.Well it may be that until he's actually seen the job, he can't be sure what he needs
I suppose yes it's a way of costing the time spent in getting the materials. But in my experience customers are more likely to feel cheated when this happens. I think it should be built into the pricing structure.
If someone has already been round to cost the work, measure up etc, I expect them to turn up on the allotted day with the materials and start the job at the time agreed. I've known guys turn up then disappear for a couple of hours or more. One has a sneaky suspicion they are indulging in a breakfast fry up somewhere (or maybe fitting in an extra little job round the corner)