The engineer who quotes is the one who turns up.
Halbrook has stayed at four engineers for most of its nineteen years, all directly employed rather than brought in as and when. That is a deliberate ceiling: bring in subcontractors to cover a busy week and the person who arrives at the door stops being someone the firm actually knows.
It means a named engineer, not a rota of whoever is free. It also means the thirty-minute call ahead of arrival actually tells you something, because the office knows exactly who is in the van and where it has come from.