It's tempting to think fresh paint will cover up nail pops, hairline cracks, and old anchor holes. It won't. A new, even coat of paint actually makes those flaws easier to see, especially with light coming across the wall from a window.
Before we paint a room, we walk it with a light and mark what needs attention: nail pops get reset and covered, cracks at corners and seams get taped or filled, holes get patched, and dents get skimmed flat. Water stains get sealed with a stain-blocking primer so they don't bleed back through.
Patches have to be sanded smooth and primed, too. Joint compound absorbs paint differently than the surrounding wall, and without primer those spots can show up as dull patches, an effect painters call flashing.
If a crack keeps coming back in the same spot, that usually points to movement or moisture behind the wall. We'll tell you if we see signs of a bigger problem, like a leak, so it can be fixed properly rather than patched over again and again.
This prep takes time, and it's often the difference between two estimates. But it's also why a well-prepped room still looks right years later.