It's virtually impossible to determine whether someone will be a good board member or equity partner. You can try your best, and some methods are undoubtedly better than others, but some people are just very good at lying.
It's not virtually impossible. Whether it is possible or not is a function of that founder's relationships and information networks. If a founder is lacking in those categories, then yes, the deck is stacked against them.
And yet, many people do it every year, over and over again, like magic.