Another option is for the PCs to be hired by someone in the government, perhaps neutrals or even a "pragmatic" neutral good or "chaotic good" individual, who has a political agenda to advance that requires that noble or king’s counsellor to engage the services of those who are prepared to break the law to achieve a higher purpose.
Ah. I love the slippery slopes theses missions present.
In these cases, the PCs are hired because they will do unsavoury things that the law abiding upstanding counsellor wants to be able to later deny. Obtaining evidence to expose another counsellor's plotting may be the counsellor’s real objective, but it may be portrayed as a more selfless investigation. Or perhaps an exposition motive can turn to blackmail in the appropriate context.
One of the possible twists on these adventures is that the PCs are often held in contempt by the good aligned noble who must hire them. The noble believes the PCs are scum (because they ususally are, after all), and that noble has ZERO problem in treating the PCs as the scum they are when their have served their purpose.
Once the PCs have fulfilled their purpose, the trail of evidence that could lead back to the person who hired them is often undesirable. Eliminating that trail of evidence may well include the eliminating the existence of the PCs. Dead men tell no tales -- and the PCs are scum to begin with. Their “reward” might well include their own deaths after they have completed the mission. If the PCs exceed the mission paramaters by killing someone, they are arrested and tried for murder, etc..
The infiltration of a cult, as depicted in the Pathfinder module Masks of the Living God may well be an appropriate assignment for your PCs. Interestingly, the PCs might choose to actually JOIN the cult of Razmir and not betray the cult as part of their own choices. It all depends.
We’ll be reviewing Masks of the Living God on Chronicles : The Pathfinder Podcast in Episode #2, expected to be released during the week of June 21.