I disapprove of pushing player to commit crimes for more than loot.
The possibility I see to give alignment value is as currency in weekly event:
The event may requires different tribute and provide different buff based on the chosen god.
For example : we sacrifice to a god of War at a Cathedral
the cost is 1 slaves, 1 warhorses, 1-300 portion of a specific 5 ingredients food...
For each participant you choose your engagement for example I sacrifice 1 additional slave for more effect, I slaughter my warhorse for mid effect or I paint my face with their blood for a small effect.
Logically the alignment would drop during that action 20,10 or 5, but for a year in game you deal 3, 2 or 1 % more damage. Having only 1 god available per month (in game) would make it a bit predictable while providing weakly event.
I m sure player would learn a bit more about the lore if they lived it.
I fear that limiting such event to the player most liked by the god in question or the pope is too restrictive but if we give them a bonus like make it cost half the alignment / pay more for good gods while providing double the bonus. This would push player in competition for the title but not excessively if a player with 100 piety can host the event.
Also I feel like we need to provide opportunity for smaller event in smaller religious building: at 90 Piety you can host the event at a church but no slaves are sacrificed. At 60 Piety you can host the event at a chapel.
You could have event of neutral god, making move alignment according to the player wishes and rituals practices, Providing a better bonus by lowering alignment.
The only bonus I would give to negative alignment character would be reducing the actual penalty or resetting to -49 min the alignment after death.
I would also reduce a character's alignment by providing incentive to ambush traders.
NPC traders could also be an entity like a coach driver or a cart puller, that spawn at 6-7 am in game carrying the goods sold at markets.
If they stop past 6-8 pm they stop for the night.
They could get raided but the initial alignment cost should be a lot (people attacking a trader should be branded a criminal for 1 h+ 1h per previous trader raided). Also raiding a trader passing by your territory should incur a triple penalty (they should appear in green).
Having multiple appearance could help us target valued goods, for exemple:
I buy for more than 600 pounds then the trader cart will need more than a small cart, but someone closer bought another 700 from the same market during the same day so a slow donkey cart is used all the way to the first then a trader cart to reach me. If the goods value is greater than 1 Gp 1 NPC guard will follow, greater than 5 Gp= 2 guards...). If the amount bought requires it I would add more cart or if the path differs it would be normal for 2 traders cart to spawn in the morning from a single donkey cart at a pit stop.