I do this very much part time and with recurring clients so I don't have a great generalizable answer. But for me, I charge a fixed price and then it's on me if

I do this very much part time and with recurring clients so I don't have a great generalizable answer. But for me, I charge a fixed price and then it's on me if there are bugs (actually, the incentives are nicely aligned here. Fewer bugs means less work for me and less hassle for my clients). As far as feature requests, I will throw in small things for free, even if not agreed upon. The assumption that I'll need to do extra little things here and there is built into my rate. For bigger things, it's important that expectations are set upfront and are clear to everyone. That way, if someone wants a new feature, they can have it for a price.