We were hiring for a payments team a while back, and two candidates looked more or less identical on paper. During the walkthrough we asked each of them how a particular provider behaves when a charge gets retried, a detail nobody could know from the outside. One answered confidently and was wrong. The other said they didn't know, then described exactly how they'd find out: read the provider's retry rules, reproduce it on a test account, and leave a test behind that fails if the behaviour ever changes. We hired the second one.
Since then every interview we run includes at least one question the candidate can't possibly know the answer to. In systems that move money the expensive mistake is rarely ignorance. It's someone quietly guessing instead of checking, and you probably want to know which of the two you are hiring.