Paint-ready trim is more than nailed-up wood. The installer has to think about how the final painted surface will read once light hits the baseboard, casing, or shoe moulding.
Joints should be tight, but the right joint depends on the location. Outside corners usually need clean miters. Long runs may need scarf joints. Inside corners often look better when coped or carefully fit to the wall.
Nail holes should be filled neatly and sanded smooth. Raised filler spots are just as visible as open holes once paint is applied.
Caulk should be used to finish small paint lines, not to cover poor measuring or wide gaps. A thin, consistent bead gives the painter a better final edge.
When trim is truly paint-ready, the room feels sharper before the first coat of finish paint even goes on.