Devil deals and soul gems

[Cyclopsw]

I have a player in my game who is wanting to trap souls using the trap the soul spell then sell them to devils and make devil deals i'm kinda wondering how this spell would effect the spell and if different peoples souls might be more valuable to a devil.

[Debihuman]

I have a player in my game who is wanting to trap souls using the trap the soul spell then sell them to devils and make devil deals i'm kinda wondering how this spell would effect the spell and if different peoples souls might be more valuable to a devil.

It makes them EVIL that's for sure. Why is this person a PC?

Debby

[arrowed]

Depending on what game you're playing, trap the soul might be quite different. I think the d&d 3.5 version works explicitly on dead people, while the 5e form is folded into imprisonment, and only works on living people.
Regardless of the PC's goodness, they're a sucker if they sell souls for mere money, and a fool if they do it with any regularity.
From what I know of D&D fluff, a devil does not care for the capture of a Lawful Evil soul in general, as it will wind up in the Nine Hells anyway. However in at least one variety of the fluff different archdevils have 'rights' to souls who are evil in different ways, so if a devil has a 'legal' way to obtain a soul for it's master that would other wise go to the master's rival, that would appeal. But the big bucks are in the souls of those who would never normally set foot in the Hells: paladins, clerics of good gods, and other active agents of good are all tempting to a devil, since they get the delicious pleasure of keeping those poor souls from reaching their final reward. Further, the fact that the soul-seller has those souls normally means a great evil has been committed to get them.
If it's 3.5e d&d you're playing, I think there was a book called Fiendish Codex 2: Tyrants of the Nine Hells, that had some rules for soul selling.
In any case, since you're running a devil, look up every sleazy rules-twisting trick you can find, and pick your favourites for the devil o try and trip up your dealer with.

[Cyclopsw]

Debihuman there is a evil player in this game who is doing this behind the partys back and arrowed we are playing with the pathfinder version of the spell also i was more wondering like if he killed a townie vs killing a level 5 adventure would
the lvl 5 soul be worth more

[Debihuman]

Debihuman there is a evil player in this game who is doing this behind the partys back and arrowed we are playing with the pathfinder version of the spell also i was more wondering like if he killed a townie vs killing a level 5 adventure would
the lvl 5 soul be worth more

It depends on the contract. The PC should probably the Devilbound Template for doing this. How much is a soul worth? Not much. The cost is in the gem holding it usually see heartstones for hags and generally souls are worth 1,000 gp per HD see soul bind spell.

[aimlessPolymath]

The value of the gem has to be 1k per HD.

Book of Vile Darkness has some uses/prices for souls:

p. 33: Souls can be used to craft magic items in 3.5, providing 10 experience points towards the item.
p. 45: A soul in a receptacle for the purpose of using it as a spell component costs 200 gp, and provides a +10 bonus to CL checks to overcome spell resistance.

Pathfinder has more nuanced prices, based on the uniqueness of the soul:
http://www.d20pfsrd.com/bestiary/monster-listings/outsiders/daemons
But there's no real "HD to value" converted which I found on a quick look around.