Wait, $400 in one afternoon? Honestly, that's a crazy fast return on a tool. I've never heard of a camera paying for itself that quick. Tbh I'm having a hard time believing it.
Seriously though, what kind of gig was it? Because a regular portrait session or event wouldn't just drop that much cash that fast. Were they shooting for a business or something? That's the only way I could see it adding up so quick.