Actually, one friend watching me said at one point: "How does Shar keep managing to get nice people following her?" To which I had to remind her that this is the same goddess that almost absorbed Sharess during a centuries long dalliance between the two and has impersonated Selune several times and luring aside her sister's worshippers that way.
She's very good at misrepresenting herself to the people she plans on wringing dry.
And evil gods prey on people's desire for revenge and the like. I love this scene in Rome where Servilia decides to devote herself to the gods the underworld, revenge and (ill) fortune:
https://www.youtube.com/watch?v=jC75FdTL2DM
