If a potential co-founder falls into category c, run a background check on them. Compromising your vision with a criminal = a bad time.
Probably 35% of all founders are out there busting their ass because
a) they want to convince the world (ie themselves) that they aren't a fucking loser
b) they're sick of people not believing in them
c) they're unemployable otherwise
d) nobody else will give them a chance