In the gaming world, a "verified" key usually refers to a license purchased directly from Steam or an authorized retailer like Humble Bundle or Green Man Gaming.
Sites may ask you to "Log in with Steam" to claim your key, which is a common tactic to steal account credentials.
While the search for a "free verified key" often leads to sketchy websites, the game is so frequently discounted that it is easily accessible to almost anyone. By waiting for a sale or participating in a legitimate community giveaway, you ensure your Steam account stays safe and your racing experience is uninterrupted.