Paint only looks as good as what's underneath it. Most of a painting job is prep, filling nail holes and cracks, sanding patches smooth, caulking gaps at trim and ceiling lines, before a roller ever touches the wall. Skip that and every patch shows through the finish coat under the right light.
Bad prep shows up in specific ways. Lap marks appear where one section dried before the next was rolled over it. Flat, uneven sheen shows where a patch wasn't primed before topcoat went over it. Caulk lines that were skipped leave a visible gap at the ceiling that gets worse as the house settles.
Sheen matters more than most people think. Eggshell hides small wall imperfections better in living rooms and bedrooms, while semi-gloss on trim and in bathrooms holds up to cleaning and humidity. Ask what primer is going under any patched drywall and whether the paint being used is rated for the room, a hallway takes more wear than a formal dining room and should be painted with that in mind.