If a customer wants to give a video testimonial for Youtube, is this verbal consent?

Consent given on camera is often considered valid consent to be filmed. However, it may not be consent as to where, for what purposes and in what ways, and for how long you may use the footage. It is best to spell all these things out in a written consent form. The person should be given time to read the form and carefully consider it. It is most valid if the print is reasonably large, the wording is clear, and the agreement is not too long. That way, people on location can read the form, know what it says, and either agree or disagree. If there is any form of coercion, the agreement may not be valid. For example, if the person has been offered a discount on the car in exchange for the endorsement on the spot, then the permission granted may not be valid. Also be aware that if person has a talent agent or is in a talent union, the permission they give may be superseded by other contracts and requirements. Your best bet is to work with an entertainment lawyer on this.

Always best to have a release in writing, no matter the purpose or the medium.