Subtle way is to get them to compare to their own other good shots. “This shot is not quite the same as your other one, XYZ. I really like the light/elements/lines, etc in XYZ, especially element A it worked much better in that shot than this one.”. If they’re as good as you say they are they will be very self-critical and go back, compare and will probably get the message.
We all make errors of judgement, we let our standards slip once in a while, we’re only human. Ultimately if they’re as good as you say they are, they will be able to be self-critical and will take the advice. I prefer it when people tell me straight out that a shot is not working, then I can at least remove it, ask others why they think it’s not working, learn and move on. If you can’t take constructive criticism how will you ever improve your craft.
