No need to warn me, I've seen the strife of having co-founders, and I've seen the harmony of having a solo found er and co-founder teams that lasted 20 years.
I don't think its a factor of finding "good" co-founders. I think unless you have known the person a long time, you can't know if they are "good" or not- its not whether they are good or not, as the most earnest, responsible, loyal and considerate founder may still be the death of your company. Its fundamental to the nature of trying to manage a company by consensus.
Consensus management doesn't work- or we'd be up to our ears in all the communes the hippies started in the 60s and 70s.