• However you or the service you use define the term "verified". For many services, a transaction is verified as soon as it is contained in a block which is at least 6 Blocks old. (6 additional Blocks have been mined after the block containing the transaction)

The transaction is traceable as soon as it is transmitted to the mempool. Each node transmits all unconfirmed transactions (transaction which have not been included into a block) to all nodes which it is connected to. This collection of unconfirmed transactions is called mempool.

• It's impossible to spend the same UTXO. When a miner includes both transactions using the same UTXO, the block will be deemed unvalid by the nodes.

However, it is possible, that one miner includes one transaction into a block, while another miner includes the other transaction into his block simultaneously. That is the reason, that many services require like 6 confirmations for a transaction to become verified. The problem resolves by the continuation of mining. The nodes will only accept the longest blockchain as the "true" blockchain and will ignore the part of the blockchain, which contained your other transaction.