In my opinion, the sealed game scene is so young that people really don't have the experience yet to tell the difference between a legitimate seal and a reseal. People at NA have tried to make lists of how NES games were sealed, but there are variants out there (known and unknown), and there are tons of people who have easy access to the kind of equipment used to seal things. I can't imagine spending hundreds or thousands on a rare sealed game when for all I know, the seller has already replaced the cartridge and manual with SMB/DH so he can dump the loose cart and manual on eBay for even more money.
Slabbing games seems even more ridiculous... if the best people in our hobby often can't tell the difference between a factory seal or a reseal, then why on earth would anyone trust VGA with it? But hey, no one will ever open up that slab or tear off the shrinkwrap to find out anyways, because they're too worried the game will lose it's value... so who cares, right?
When we're reduced to trying to judge the age of plastic, or trying to look for signs that a box flap may have once been opened, then I think we really need to reexamine our priorities in this hobby.
--Zero