First, I would make sure I was calm. Then make the phone call. Gentle conversation asking if your concerns are with the machine itself, or the way the machine handles and it could be checked over and adjusted to your satisfaction? If it can't be resolved with that particular machine, I personally would make sure to mention that I am interested in another machine from him or the business, and what would he suggest? If possible, test it out before agreeing to anything. Working with the person makes a bigger impact than working against him. Good luck to you! Don't settle. You sew because you love it, you should really enjoy sewing on the machines too.