As everyone has already stated:
Too big or too small.
Too heavy or too light grind.
Custom blades and scales where the maker ignores (or doesn't know about) esthetics and tries to cram as many gimmicks into the piece as possible.

If it's from 9/16 to 13/16, 1/4 hollow to full hollow and it doesn't look like a prop for the alien from Predator, I'll probably like it.