Great comment.
I get pitched a lot to be a technical cofounder, and I put a lot of thought into assessing the biz skills of a potential sales/marketing/bizdev cofounder.
As you said, some ideas may be better suited to having someone with a sales background as a co-founder while others for someone with killer marketing skills.
And I've also found in the past that I have a different working dynamic with sales vs. marketing people as they often complement/overlap my skillset in different ways.
Another random thing to add regarding founder dating from the techie side is an awareness if someone is giving off the vibe that they're really looking for their first engineer even though they say they're looking for a true cofounder.
Finally, I try to distance the individual from the idea and ask myself, "Would I want to still co-found something with this person if things don't work out and we have to do a hard pivot from the original idea?" I would rather team up with someone great on a marginal idea that may evolve into more than someone just because I think the idea is killer. Most people I know in Silicon Valley have a million ideas on the backburner anyway, so it's a red flag to me if the idea interests me more than the person.