I'm working for a startup where the primary founder did not perform enough due diligence on his co-founder and the results have been disastrous.
The co-founder constantly brags about his employment history at major tech companies in the area. Only later did we all learn that: 1) His roles weren't as important or high-ranking as he claims and 2) He was fired for non-performance from his last two positions. Both of those points are becoming big thorns in our fundraising as investors want to speak with both founders' former bosses.
This co-founder did work hard for a brief period when the company was started and managed to produce some good initial funding. But when the funding hit our bank, he became a victim of his own success and spent more time empire building than working on the company. Within months of our initial funding he was already working his way into adviser positions with local startups and spending our marketing budget on having a PR firm get puff-piece articles about him into major publications. I think he's spent less than a thousand dollars on customer acquisition and advertising for our product.
He rarely comes in to the office any more, and when he does he can often be found watching ESPN or Hulu in the conference room. He some times doesn't even bother to stop watching his sports games on his laptop with his headphones over one ear while he's supposed to be leading team meetings. It's depressing for the entire office, and we're losing people left and right over it.
The takeaway here is that a bad co-founder can easily sink your business. A bad co-founder isn't immediately obvious. In this case, the person in question is charismatic and persistent when necessary, and has a great ability to sell himself to others in the short term as long as you don't dig too deep in to his spotty past. This was great for securing our early angel funding and dumb money, but once the company tried to secure real funding from the big league VC firms the professional investors saw right through his BS.