Here is a good place to ask questions or over at the Blades in the Dark forum. So, thanks for asking and no the paid Grit was not meant to be permanent but a one-off payment. I hope for a good scene when the PCs is bounded the artifact (or the other way around). Maybe the PCs does not choose the moment for the bounding but the artifact does or the former owner dies in combat and you have this one chance to snatch this Hellstone gun before some else does. If you don't have enough Grit left or you just don't want to accept a Stigmata you may choose to resist. BTW if you resist or not does mean something storywise, right? Open arms acception or another burden, it may establish a starting ground for this PC/artifact relationsship. Everything is a good story or questions to the players or a cool scene.