[mothered]

If I want to use this card for others SEs on amazon, would a new account with the same card be better, or I can just continue to use this?

They can Identify your card with every transaction made, so It's better to create a new account along with a new card.

The fact they check sealed boxes isn’t a big problem if they check AFTER they already refunded you, and if you don’t care about the account and have no money on the card obviously….

If they really want to take It further and retrieve the funds, they can simply send/email you the Invoice.

Of course, It's not a problem If your Amazon account was created with fake credentials.