When verifying transactions, nodes and validators check that they are:

1. Valid: Ensuring that transactions are correctly formatted and follow the blockchain's rules.

2. Correctly signed: Verifying that transactions are signed with the appropriate private key, ensuring ownership and authorization.

3. Unique: Checking that transactions are not duplicates or already spent.

4. Authorized: Verifying that transactions are authorized by the sender and recipient.

5. Compliant: Ensuring that transactions adhere to the blockchain's consensus rules and protocols.

6. Properly constructed: Verifying that transactions have the correct inputs, outputs, and metadata.

7. Not malicious: Identifying and rejecting transactions with malicious intent, such as double-spends or fraudulent activities.

By verifying transactions, nodes and validators ensure that:

1. The blockchain remains a trustworthy and reliable ledger.

2. Transactions are secure, valid, and authorized.

3. The integrity of the blockchain is maintained.

4. Users' assets and data are protected.

5. The blockchain's rules and consensus mechanisms are upheld.

Transaction verification is a critical step in maintaining the security, integrity, and trustworthiness of the blockchain ecosystem.