A candidate was halfway through our take-home review when they stopped to ask which number was the real one: the balance shown on a user's account, or the sum of the transactions behind it.
Nobody had asked that before. We were treating the exercise as a coding test, and they read it as a reconciliation problem, which is what it actually is in production. Two places show money, and if you have no stated rule for which one wins when they disagree, someone will eventually pick the wrong one in front of a customer.
They were right, and it cost us an afternoon of embarrassment plus a rewrite of our own task description. The ambiguity was baked into it, which means every earlier candidate had quietly guessed instead of asking.
So we left the gap in on purpose. The only thing we really score now is whether someone asks about it before they start building.
We'd like to hear the question you wish more candidates asked you.