I was at one of my go to dealers one day and I was looking at some of his gold, raw and graded coins. I was looking at a AU 50 Liberty 2 1/2 in a old NGC holder. He asked me what I thought and I said the new slabs with the corner pins show the coin nicer.It was a bit scratchy and the soap bar look overpowers the coin a bit compared to its size. Before I could make him a offer he took the slab and a pair of cutters and snapped it out of the holder. I said wow that was quick and he said I trust your judgment as a collector and I will get the same or a better price for it without the slab. So Yes ,,People remove coins from slabs all the time even professionals.