what do patrons take
It depends on the patron. A patron that is evil (like I imagine most are) would offer you a deal that sounded great, but had some sort of a mechanic in it that made the terms harder and harder to meet, like compounding interest, so that you had to scramble not to default on your debt. The more desperate you are, the easier you are to control.
Maybe a glutton patron that required more and more exotic or formerly sentient meals from a chef. It should seem innocuous at first, and then slowly unveil the horror like soylent green.