Would it be trivial for someone to dispute the authenticity of the coin, receive PayPal's request for its destruction, photograph something that looked like a mangled coin, and then essentially get the coin for free?
1) Get the original (say, $3000 coin) carefully out of the holder - then smash the holder with a hammer.
2) Find a replica of that year coin, which really is a fake, for $10-$50. Scratch it up, bend it, whatever.
3) Send the original coin back for grading to be certified with a new graded coin holder and serial number, to be sold for $3000.
This is just the "kill them all and let God sort them out" mentality applied to property.