The correct way to do it is to have them get (or you get) a temporary trip permit. They last for three days in washington. They can get their own in the state they are traveling to when they go deal with inspections or license it. You will need to give them a bill of sale, the signed title and file your sellers report if your state requires it. That last one is important because it releases you from liability as soon as it is filed. Just contact your local DMV ans ask for a trip permit. It should only be a few bucks.
