There are two types of nodes: Signer nodes, which can validate and seal (approve and sign) the contents of each block, and Transaction nodes, which share the same blockchain data but cannot seal it. The Validator node is a trusted node, and is responsible for signing (sealing) the block when its turn comes, while building consensus through PoA. If the Validator node cannot be trusted, the reliability of the block for which it is responsible for the blockchain data is questionable.