Mark has given you outstanding advice. The only thing I might add s to always discuss the specifics ahead of time( which includes the goals of the project and the uses of the video. Then create an agreement that details every item. This is just as critical to do with friends and family as it is with clients.
At the end of the day, your friend has every right to do what he wishes with the video. He also has every right to charge what he feels he can get. You have the same right to charge what you feel is adequate.
If you want to make an agreement that includes a percentage of profit for each video sold, both of you can discuss this and reach some sort of agreement.
But really, you have no control over what your friend does with the video. As Mark so eloquently said, you are part of a work for hire project. Your friend has every right to refuse any type of percentage payoff.
I have a client who manufactures and sells devices for $5,000. I charge him less than that for a video. I never ask for more than the cost f the video project.
Maybe you’re not charging enough for your service. Maybe you’re friend is a great salesperson! Either way, since you’re friends, it can’t hurt to ask. Then decide if you still want the work or not.
Greg Ball, President
Ball Media Innovations, Inc.
https://www.ballmediainnovations.com