You are playing 2/1 with a pick-up partner, who you know to be a advanced but not expert player. LHO is a national champion and RHO is his expert partner, who you are playing against in a club game (matchpoints) of a mixed standard. Everyone is NV.
RHO opens 1♦, you pass, and LHO, not seeing that his partner has opened, prepares to also open 1♦, but then changes his call to an inverted 2♦ (the original call not having left the box). Partner bids 3♦, presumably Michaels, and RHO reaches for a double card, then puts it back and instead passes to you.
You know both of these players are very ethical, and will try and avoid any actions suggested by the UI.
What actions would you have taken if there had not been any UI flying around? Does that change with all of your extra "table feel" available?