my honest advice is dont bother, they give you a fixed price and most of the time material is included in the fixed price (there is some negotiation, but not much leeway given to you, swings and roundabouts they tell you) they squeeze you really really hard, and a lot of jobs require 2 visits, 1 to see whats needed then 2nd to repair, they try to get you to invoice only 1 visit, and never pay travel,