You'll need at least thirteen attempts to assuredly open the safe.
We have three keys and three locks, and so we have six different ways we can arrange the keys to assigned locks. Depending on how they're arranged, one of five things can happen:
We also have three locks in two possible states: locked or unlocked. We therefore have eight different possibilities when it comes to how the locks could start off as. And because we don't know how each lock was at the start, we have to go through ALL possible combinations to guarantee the safe opens. So we can't do any better than eight tries, but we can make sure we don't do worse than thirteen. Try opening it by inserting each of these keys in the locks ordered 1-3 in this order:
ABC, ABC, BCA, CAB, ABC, BCA, ABC, ACB, BAC, ACB, CBA, BAC, ACB.
More than just one of these could happen at a time.
It... doesn't really seem plausible .