Even after reading all the great material here I made the mistake last season of buying boots too big. The classic beginner mistake.
Not just one size too big, but 2 sizes too large. As you all have mentioned many times - the only way to test is a shell fit which I didn't do when I bought my original boots.
This weekend I have recified my mistake and bought the same pair of boots (Lange Blaster Pros) 2 sizes smaller (25.5 for a street size of 10) instead of the 27.5 clown shoes. I can fit exactly a normal sharpie (about 15 mm) behind my foot with the liner out. I still had trouble believing this was the right size for the first couple days since the fit was so tight. Finally after wearing the boots around the house for about 12 hours the liners are packing out enough for my feet to be comfortable (although still snug).
I can't wait to hit the slopes this season with boots that fit! I wish I had paid more attention to what was said here earlier. Now I have to find someone with big feet to sell my old boots to :P