Last weekend when I was at a coin show I saw a very nice circulated standing liberty quarter stabbed in a PCGS holder. It was an early but a tough date. All looked great until I saw a green spot on the reverse. I was not sure it it were PVC or something on the coin. The dealer thought the spot was benign but i was a little paranoid and passed for another day. Have any of you seen any potential PVC spotting on a slab bed coin? Would this alter you from purchasing this?
Without a picture we can not give specific opinions. But if you are unhappy with the coin you took the correct action. Don't buy.
Although it's quite possible for silver to develop verdigris - and happens all the time - as a generality if I see something green on silver which obviously isn't toning, the assumption is it's PVC plasticizer nastiness and the coin is either a pass or gets cracked as soon as I own it. There's no guarantee it was green when the TPG handled it, because the early stages of the infection don't show that color, although there are plenty of examples of slabbed coins which were plainly infected when they were slabbed. "57th Street Hoard," I'm looking at you.
