People tend to choose a decorator on the colour and the price. But the thing that decides whether a finished room looks considered or rushed is the bit nobody photographs: the preparation.
Here is why. Paint is thin. It follows whatever is underneath it. If a wall has filler that has not been sanded flat, old flaking paint, dents, or a skim that ripples, the colour goes on and shows every bit of it, especially in daylight from the side. A second coat does not fix it. It just gives you two coats of the same problem.
Good prep is unglamorous and it takes time. It means filling and sanding until a wall is genuinely flat, not just touched up. It means caulking the gaps where walls meet trims so the lines are crisp. It means priming bare or patched areas so the topcoat sits evenly instead of soaking in here and sitting proud there. And it means protecting the floors and fittings so the job does not create a different mess to clean up.
This is also the real advantage of having the same crew plaster and then paint. When the team that skimmed your walls is the team that decorates them, the surface is right before a brush ever touches it, and nobody is painting over someone else's rushed prep.
When we price a job, a fair chunk of the work is prep, and that is deliberate. The coat of colour is the easy, satisfying part. The reason it looks good afterwards is everything that happened before it. If you want a finish that still looks sharp in a year, ask what is included in the preparation, not just how many coats you are getting.