There is nothing wrong with Coats & Clark thread. Except that you obviously didn't buy your thread from her, therefore she thought she'd make you feel small in order to make herself feel important. I'd go out of my way to avoid buying anything from her shop in the future, or using her mechanic--unless he wants to repair your machine at his home without the shop owner knowing about it.
BTW There is a local Bernie dealer and repair man in the next city who is the brother of the owner of the quilt shop next door. I won't go there because the two stores are in a partnership and the quilt store lady is very rude, as if since you don't shop there daily you are wasting her time. The little quilt shop with the Janome dealer inside has always tried to be helpful, even staying open a few minutes late for me to search for something, so she gets my business when I can make the drive there. Debra in VA See my quilts at