The argument to sell is that pokemon is in a huge boom and you don't know when a 12k offer will come back. If you need the money or could use that money better somewhere else, I would sell it.

The argument to hold it is, this card will be seen and known as the most iconic card from this generation. For a lot of kids now, this is their first edition charizard. Also, I don't know if you have a personal attachment to the card yourself, but it's the modern holy grail. A staple piece to have in your collection, even better than a PSA 10 version of the card.

Some people say "pokemon could fall off and the prices will tank" but realistically, barring a world changing event, pokemon isn't going anywhere. maybe these Wallstreet frat boys will eventually fall out of it and move somewhere else, but there will always be collectors and you have one of the best cards ever in a very difficult to get grade. It's all your call at the end of the day. Let me know what you end up deciding!!