I got mine used from a dealer and they came out & set it up. Mine seems very sturdy. I'm not exactly understanding what you mean by the roller bars being flexible so your quilting is crooked. Can you elaborate?
The issue I have with mine is the track that the wheels run on deteriorates and although you can get replacement tracks, you have to disassemble the entire frame to install them. When the track is damaged, the machine won't move smoothly over those areas. I pretty much know where they are and just get a good grip on the handles when I get in that area. Other than that I haven't had any problems...