I haven't had many paint disasters, except this one, luckily it was on my own home. For clients homes, I specify and it works. I don't even do wall swatches.
Whether you're choosing paint colors on your own or with a designer here are some tips for making sure that you avoid a disaster.
1. Good quality primer, paint, and tools. Bad brushes can leave strokes or bristles in the paint. Bad paint and primer won't cover properly.
2. Two coats of paint, if the color seems right after one, fine, but usually it takes two.
3. Careful of color matches. Some places are better than others. If you're a stickler, it's better to stick with the same manufacturer for color & paint. Meaning, if you select a Benjamin Moore color, use Benjamin Moore paint.
4. Alright, you can do swatches. Choose no more than 4-5 paints to swatch. More than that and you'll drive yourself crazy. At least 2' x 2', two coats, and on a few different walls. If you have a strong base color it can affect your samples, maybe prime first in that case. If you are going to do swatches, it should be on the wall. Yes, you could do it on another board or paper, but the texture of the walls makes a big difference to how light is reflected and how the color looks.
5. If the painter puts the color up and you feel it is wrong, ask them to stop. Request that they complete one wall with two coats and sit on it. Put your blinders on (so you can't see the other walls) and look. Either the color is wrong or it could be fine and you're reacting to the change or the interaction with the unpainted walls, or two coats are not up yet. The good news is paint is inexpensive.
What about you? Any paint disasters? Any tips on avoiding disaster?
PS: Here are some guides to help: