I believe I would tell them. OK, I'd like to think I'd tell them.
Unless they had recently screwed me over in some way, then I might consider a tit-for-tat.
Seriously, I believe I would. But only once, and only if it did not inconvenience me (did not involve any 'work' for me)*. If they did nothing about it I would not persist.
*To show what I mean by that, here's a story I heard a few years ago. A guy checked his bank balance and found a
very large amount, which was not his, had been deposited into it. He rang his bank (CBA or NAB, can't recall which) and told them about it. The bank employee said "Oh I see Mr Smith, you'll need to go to your branch and..." He was cut off by Mr Smith who quite reasonably said "Excuse me?
I have to physically go to the branch to rectify
your mistake? I don't think so"