The motivations on each side of claim sales are different, but complementary. The seller either needs immediate cash to meet bills, wants to write down their losses for tax purposes, or believes they can earn a greater return by investing the money elsewhere. The buyer, meanwhile, is wagering that the value eventually returned to creditors will exceed the amount they paid for the claims.

Claim sales have typically happened behind closed doors, taking place between financial institutions. But over the past few years, public marketplaces for…