What's the FFG policy on trading decks among ourselves? Can we use the code, play our deck for a while and then sell the deck to someone? Can that someone then register that deck and play it in official events? If so how will FFG deal with claims of theft (i.e. I sell the deck I registered to someone and then after that someone tries to use it in official event claim the deck was stolen)?

It sounds like multiple people can have the same deck scanned, but only the first scan gets the aember shard.

Only one person will be able to play a deck at any event, and it should track the results to anyone who has that deck scanned.

In other words, you could trade a deck from someone and it will have any chains and power levels that deck has earned at events.

Use the app to look up the information before the trade takes place.

FFG is fine with trading decks based on everything I have seen. They even mention that chains stay with a traded or sold deck. So yeah, you can use a deck, then sell/trade it no problem. Though be sure the person who is receiving the deck knows if the Aember Shard has been claimed.

The theft issue is moot. You having a deck registered does not mean you own the deck. It just means you scanned it into your app since decks can be bought and sold. You would go through legal processes if you want to claim someone stole your deck and your only proof is you have it registered to your account(and then the legal authorities will laugh at you and tell you to move on with your life).