Are we talking European souls, south west Asian souls, or East Asian souls?
I’m pretty sure Daoist, Buddhist, or Hindu souls are not sellable conceptually in the way European souls are. One of those times when ‘無門關’ (mu-koan) might be the right answer. Not really a thing, in the western concept anyway. Anymore than it’s possible to square a circle, or calculate Pi from a line.
Maybe that’s why European cultures have been taking over the world? We were able to sell our souls to the devil?
Muslims seem divided on the topic (among many others), with a pretty solid ‘western’ type tradition of ‘you bet, but you’ll regret it’ to a similar type view of the Catholics near as I can tell (no, and you’ll be forgiven if you get back on the right path).
I guess it behooves one to familiarize oneself with something one is willing to take as collateral, eh?
P.S. If you’re an atheist who doesn’t believe in a soul, then clearly you’re a soulless bastard. ;)
(Leaving out the extremely wide variety of African and various covered regions indigenous peoples Soul-concepts for brevity).
This goes somewhat deeper than you might expect. "Literal" spells are for sale on e.g. ebay, and presumably authenticity/belief are managed like reputation?