People are often advised to show the lowest necessary card for fear that they will be asked to do things, like take on a beginning diver. I have never seen or even heard authoritatively of that happening. Dive operators generally want their customers to be happy, especially the ones most likely to return or recommend them.
In my experience, it is quite the opposite--I show an instructor card, and I get treated better, including not being treated like a beginner. My problems along those lines have been because I got on the boat with a crew who does not know me or my training level because I signed up for the dive without them being around, and I end up getting assigned to beginning dive buddies because they didn't bother to check.