Well, among his options if he ends up uncertain are to request a compact like that with Lrilatha, and see if she's mysteriously in Hell and can't get back until tomorrow. Gorthoklek will of course also be unavailable, nor will they be able to summon whichever devil supposedly bought Carissa's soul...
...phrasing it as 'buying souls' is starting to make him more nervous, after seeing the slave market in Absalom. You would think, people would not phrase it that way, or would find some way to rephrase it more reassuringly, in a world where slavery was also a thing. Maybe Hell phrases it that way, because nobody in Hell is worried about slavery, and the mortal world follows suit...
...that slavery market really didn't look like a place that people could escape, just by walking out of Golarion, and into an afterlife where you buy consensual enhancements over thousands of years.
He was supposed to be listing out the evidence incongruous with Conspiracy. Not starting to connect the pieces together, until he made sure he had all of them.
It no longer feels to Keltham like he'd be defending his world disintegrating, by doing that. It feels like he'd just be delaying the destruction-by-truth, delaying the pain, for longer.