I started a job a few months ago. I received a 50% down payment with the balance due upon completion. Scope creep inevitably occurred:
Me: I'm happy to add these features, but I'm going to charge my hourly rate in addition to what we agreed while implementing them.
On Monday I sent the final invoice to no response, then sent a follow-up email today (April 5).
Client: Oh. We didn't respond because we thought that ridiculously high invoice was an April Fool's Joke.