What specific tactics,questions did you use to measure how/if people can get shit done,have a positive mental attitude, and actually have a passion for your concept. There are many other things that go into identifying whether a co-founder is a good fit or not, but I assume it should be somebody like me, which is very difficult to find.
You want to have the foundation solidly covered, by people you feel have a broad awareness / intelligence, but deep expertise in core startup skills (for most tech startups its hustler, hacker, designer) and the industry vertical.
In my experience working with amazing, quality people eventually eclipses all other concerns – so "passion for your concept" is less important than it appears.
My personal yardstick is if I can disagree with someone but still feel that their opinion is really wise, informed, considerate, teaches me something, etc.