Man come on, what kind of trade is that?
What do you mean what trade is that? Most of all religions also base themselves on serving the god, or follow a proper way of life for all it to be accounted in an afterlife. It's literally the same, but in this case the god, or should I say the goddess, is right here in front of you.
She manipulates this people making them think she really is a goddess and that after they are eaten by her, they will go to some kind of paradise or bulshit like that.
So you do not mind believeing that GG world has a bunch of gods, existing heaven and hell, spiritual powers, freaking magic, but when some almost omnipotent living being says that she can store souls of her followers for them to be together for eternity, you go "nah"? She may not be an actuall goddess by GG world rules, yes, but does this make her less powerful? No. Does it deny the fact that she can actually do what she described for her followers, considering the fact that necromancy and magic of life is a thing? No. Yes, her cult is twisted, but it's just unfair to draw her as liar just because she is "evil".