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 have to be careful on selecting your co-founder. I know it's an already cliché to mention it, but selecting one is like selecting a spouse to marry.
You need to know the person first, and even some investors and accelerators dismiss automatically startups because the founders didn't meet before working together in the startup.
If you're doing a tech startup, the co-founder should have a technical background if you don't have it. That will save you a lot of money when you're bootstrapping as well as making sure you deploy a great product as soon as possible.
Once you want to work with someone, my best advice is to hire them to do a project or a task inside the startup. More than words, you need to see them in action and that way you can evaluate your chemistry as a team.
When you already worked the details and decided to create a startup together, you need to be smart about the plans. You need to sign a partnership agreement and put the equity in a vesting option.
In Silicon Valley, the standard vesting period is 4 years with a one year cliff. After one year, the founders fully own of the 25% of their shares. That means if they leave the company before the first year, they will not have equity in the company.
Having all that in mind, I think it will help you select the best co-founder possible and also be a better bet to investors if you ever decide to raise money. I hope it helps!
Understand their background and ask them to give examples of what they did. Ask questions that define their character. Ask them what their goals are and why they would want to be involved in starting a company. Do these things align? If they do, agree to do a three month trial period to see if you can actually work together.
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.