I watch the videos.
I have determined my goals beforehand, so I see if the tutor / teacher can meet those goals.
I check to see how well I can understand the person. If I can't understand the person, regardless of ow well they may teach, it won't be beneficial to me.
I check the availability for teaching. I have certain hours in which I am able to take classes. If the classes cannot be held during those hours, I cannot use that person.
Also, what did I take away from the initial lesson? Was it useful, and will it continue to be so? Is the teacher / tutor interested in helping me learn?
Do not give out personal information. Skype ID's will be given once the person signs up for a class. Not only is it a dangerous thing to do, it could be against the teacher / tutor rules.
Personal data sharing with a stranger is a bad idea.