I have had to fix my PCGS slabbed coins because they will rotate in the slab from vibration. All you do is tap the corner of the slab on a desk or something hard and it will rotate pretty6 easily so this is definitely nothing anyone could dup0licate themselves and I bet it was straight when PCGS put the coin in the slab. Whoever buys it should tap it around and send it back for not being as described
Edit: I see jakedacc already mentioned above that this is easy to do