In my experience, transparency is key.
Be polite, transparent, and most importantly... DIRECT when things hit outside of the scope.
It's okay to set boundaries and let the client know.
They may have purchased your gig... but at the end of the day, you're allowing THEM the opportunity to work with YOU.
(On a related note, there's an elephant in the room we should address. Even with perfect communication and boundaries, a client pushing beyond scope can still leave a negative review post-delivery, refund or not. It's a flaw in the current system that makes enforcing these professional limits you're advising about feel risky. So... while this advice comes with good intentions, it doesn't quite capture the full reality that reputable sellers face. The challenge lies not just in setting boundaries, but also in the potential consequences of enforcing them. And unfortunately, all of this falls on the seller and Fiverr doesn't protect them at all.)