Whole-house estimates should identify exceptions room by room
A bathroom ceiling, vaulted family room and flat bedroom ceiling may not behave the same way. Ask the contractor to note painted areas, previous repairs, water stains and unusually high sections rather than giving one blanket assumption for the entire house.
If a company proposes covering some ceilings and scraping others, have the reason documented so you understand why the methods differ.
The best quote explains what you will see at the end
Look for a written finish standard, not just “remove popcorn.” Confirm repairs, skim coats, sanding, primer, paint and cleanup. Ask how the contractor checks the surface before applying the final coating.
If the ceiling material is older and unknown, handle any appropriate testing before demolition. The project schedule should account for that step.