This is an effect I used to perform 10+ years ago. Maybe even longer ago than that. It bugs me that I cannot remember the details of it today. I'll describe what I remember.

First of all, it is not Danny Archer's 'Eye Exam' trick.

In the trick I am thinking of the magician does a sequence of observation tests with a volunteer using 4 cards. I think there are three stages plus a final revelation. Each stage features a question, like how many black cards are there, what suits, what are their faces. Maybe one of the questions has to do with the back colour of the cards. Or how many cards are face up. I don't remember for certain what the three questions were, but I'm pretty sure there WERE three. Each time, the volunteer is shown to have made some error.

I think the final revelation is that all four cards have changed into something other than what they were. Say, aces instead of fives.

It reminds me of NFW but I think it was a different commercial packet trick.

HA! I found the answer in a thread just below. It is Jon Allen's "Double Back" I am thinking of.

I misremembered some of the details, but that IS the trick.

Thanks to Mb217 for that thread.