Here is the delicate part. She’s convinced him, yes, but it’s the romantic part of him that really wants to do this, not the mercenary part. And it’s the mercenary part that must needs be convincing. Or at least appear convinced. So - something that he can look like he’s being sensible about. Or a dick about. Or both. Maybe a little of both.

He faces her squarely, meeting her gaze with his own. He is being honest at least - or at least he’s being honest about the important parts. “Collateral,” he says. His own hands are warped and cramped in her grip. Hardly graceful. “Something valuable to show you’re serious.” Here he lets his gaze drop to he sword she’d brought. “I’m a collector of novelties, you see. Even got my hands on a Barrayaran deal dagger from the Time of Isolation.”

Let her think she’s some crazed collector who will try to steal a piece of her history. He’ll return it in private when all is done.