It's debatable. In a way you'd ofcourse have to showcase your skills but at the same time I don't know if the bikes assembled by prospective employees are sold as is directly after the "interview". I am also unsure if their business is willing to take that chance to run the risk of their customers purchasing bikes assembled by people that haven't been check for proper credentials?
But I do see where you are coming from. I worked as a mechanic with no formal training or credentials to back up my work but I did have to undergo a few series of showcasing where I had to service drive trains, then the next visit would be for a wheel build, and the next for a brake job mind you this was on a bike that all prospective employees had to work on, not a bike fresh out of the box.