You really think the best way to start a new business relationship is with the assumption that the guy across the table is a lying scumbag?

I am not sure I understand your position. So you would not get a lawyer to review a business contract because doing so would imply that your business partner is a lying scumbag, a morally unacceptable position when starting a new business relationship?

No, and that's called due diligence. Same with hiring. I have come across enough candidates where there was a huge gap between claims written on the CV and what the candidate actually did or knew to blindly trust any CV.

And the best candidates are often not the best CV writers.

You start by assuming they may be a lying scumbag. Hopefully by the time you make an offer, you're reasonably certain they aren't.

And somebody putting only lies in a resume will turn super honest on the phone?

No but he wouldn't be able to answer questions that go a bit deeper into what they claim they did or know but didn't/don't.

Yes. And that this kind of discovery - especially detecting if they lied at you in written text, which for me is an exclusion criterion - requires having read the text...