Hm, they have an indication in your Timers when their ventures are done, as well as when the Squadron is back from their mission ... but otherwise, eh.

If you are playing you can see when something sells in your chat window (unless you are in a dungeon or instance), but in truth it really only takes a second to check your retainers.

Not dismissing your suggestion in any way, but from the way Squeenix has been, I don't think they will do it ... or suggest you get the app on your phone to check (which will show what was sold).