Question: What happens when a transaction is included in more than one block?
Don't break the forum rules,and no PLAGIARIZING!
Only one transaction will be considered valid (the one which gets included in the block that is broadcasted first on the network). The other transaction (and/or block) will be considered invalid and will be rejected by the nodes.
Source:
https://bitcointalk.org/index.php?topic=216938.0Actually, there is no first mover advantage when it comes to transactions, or more precisely said, not anymore. Double spending with a higher fee will make sure the later transaction confirms before the first one.
It's all economics based, where miners only confirm transactions with the highest fees, especially in times where unconfirmed transactions are piled up and impossible to confirm by the next block.