It is not possible to legally run a license plate number in order to find information relating to the owner of a vehicle. This applies whether the license plate look up service is free or paid for. It is, however, possible to look up a license plate to see if it is available for purchase.
Only members of law enforcement are legally permitted to look up the owner details of a vehicle using the license plate number, according to the DMV. It states that there are services available online, but they are often scams. CNET also published an article about a court case where it was decided that individuals do not have a Fourth Amendment to prevent their personal information being searchable via their license plate, providing the search is done by law enforcement officials.
It is legitimate and legal to lookup a license plate number, when a buyer is looking for a custom plate. They can use a look up service to find out if the plate is available for purchase. The DMV websites of most states offer a service that allows users to check if the license plate that they want is available. The DMV New York website offers this service, for example. In addition it provides information on the types of license plates that can be registered, and under what circumstances.