What's the best way to color match your paint?

The paint supply house I use has a scanner. They will come out to the car, scan the paint in a couple of places and go back inside and mix a paint to match. Works well on solid colors, it gets it pretty close on metallics.
I always try to get a few opinions when I'm not sure of something. My paint has a slight metallic flake to it and I was hoping it could be matched pretty close. Yes, the scanner is an option but, as you stated, metallic paint is a bit more difficult to match. Yesterday, I was given a number of a women who is a pro on matching any type of paint. MMG