Interior painting in Toronto often starts with what earlier coats left behind. In the older semis and row houses east and west of downtown, walls are plaster over lath, trim carries decades of oil paint, and no corner is quite square. I read the surface first, then decide what needs a bonding primer, what needs filling and what can be sanded and coated.
I do the work myself, so the same person quotes the job and finishes it. Furniture gets moved and covered, floors get protected, and I use low-odour paint so you can stay in the house while I work.