I'm guessing this is a Viking store? Why does it have to be a Viking machine? I think you can say that the class will be taught using a Viking machine and advise that the class will be taught by a Viking employee, but if I own a Bernina and have a good knowledge of my machine and feet, I think I can attend. Besides, if I know my Janome but see what the Viking can do I might want to buy a Viking machine. I don't think its right to restrict this to Viking machines or any particular machine. The person can stop in and be screened for knowledge before the class if your worried about it right?