Seth works as an auctioneer at the Black Market, where he's basically the guy running the show when it comes to moving merchandise—or in this case, people. He's best known for convincing Chise to sell herself into servitude, pitching it to her as finding someone who'd actually appreciate what she is. Whether you see that as opportunistic or pragmatic probably depends on your take, but Seth clearly operates in the moral gray zone the Black Market thrives in.
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