I had this weird ethics problem arise. Partner opened 1♦ in a field that he knew well against opponents he knew well, but I knew no one at the table except partner, of course. My RHO passed. I responded 1♠.
LHO now pops in with 2♠, and partner bids 3♥.
It seemed to me that 2♠ should be natural, but a lot of people play this as Michaels. Looking at my hand, I guessed Michaels. But, no one asked any questions. This became troubling.
If I asked, I would have to assume, it seems, that partner already knew the answer and acted upon that knowledge. However, by asking, I would be advertising (possibly) that my spades were very good (making the normal meaning suspect). So, I assumed that which seemed obvious (Michaels) and bid accordingly, without asking questions.
As it turned out, humorously, my partner did already know their agreement -- natural. However, LHO had forgotten their agreement and bid 2♠ intended as Michaels.
I had assumed that 3♥ was a power raise of spades; partner meant it as hearts. I cuebid 4♣ as a courtesy cue (and admittedly as a hedge), and partner bid 4♦ (which I took as a cue). I bid 4♠ as a signoff, and partner bid 5♦. I decided that this was a cue, but I bid 5♥ as Last Train (secretly hoping that partner had 5♥/6♦ if I was wrong, and some serious playing skill).
5♥ scored poorly.
I think I did right, ethically?