tbh I don't like the trope of "pact with a devil = you sold your soul". At least in the first instance, even very desperate people are usually not desperate enough to literally sell their soul. Not in a world where you know that souls are very real and selling it has eternal consequences.

Most often, a pact entails something much less. A favour of some sort, either a specific negotiated deal, or a general agreement to do "something" in the future (think: the Minor and Major Boons from Vampire: The Masquerade). That goes whether we're talking about a warlock pact or some other pact.