I know good seeds are dark, not cracked etc, but I heard that if you try to pinch/break it with your fingers its no good...is this true?
If the seed crackles when you roll it firmly between your thumb and forefinger then most likely it is not viable.
Plumpness, stripes and spots or lack thereof don't matter, these are genetic variations that do not tell anything about the viability, potency, gender, or anything else about the seed.