Having trouble after card show

I got home from a card show, and I am taking account for everything I sold. I am missing cards that I do not have numbers for, one table stands out in my memory, this guy took my cards from the binder and put them inside his slab case, where we both could see, but he lined them up almost perfectly to wear a card would be inside a slab, so it looked like my card was inside his already own slab if that makes sense, we did a couple of deals and I ended up calling out when I noticed it the first time on our 3rd deal, he said it wasnt intentional, but I feel like it was, im going to confront his about it or watch future deals since its a local card show.

To better explain the illusion that was intentional or not,

He would take the card from my binder, and it would sit directly on top of a slab he owns but right in the middle where a card would go, it would blend in with all the other slabs, when adding up prices I would miss the card since it looks like its in his slab

was this a hustle, has anyone seen or notice what I am talking about