STAND YOUR GROUND! I've owned three Berninas and one Burnette in the past 7-8 years. The Burnette was my first, and it went up in smoke (literally) the second or third time I used it. Fortunately the dealer was embarrassed and gave me a decent (I think) deal on my first Bernina. While it has its limitations, this machine is still my primary.
When my husband and I bought a second home a few years later, I bought a used Bernina off Craig's List. It never did sew well. After taking it to my local Bernina dealer for the second time in ~6 months, he confessed that this model had never performed very well. So I traded it (+ $) for another model. While we don't spend nearly as much time in this second home as we'd imagined, the machine is sewing well for me.
Bernina's are very pricey, and they're supposed to be the best. But sometimes they aren't! For the sake of us all, please complain and demand that your machine deliver the quality you paid for!!!