Can a contractor lien the property and my vehicle?

Yes and no. The contractor can file a lien against your house for non-payment. Even if you honestly don't owe the contractor any money, he may still lien your house; he will eventually have to prove the lien's validity in court or it is automatically released. No lien can be filed against your car. However, if the contractor gets a judgment against you, that judgment may be executed against your car and home to secure payment.