I started with a very inexpensive machine (bailey) that is basically a stretched domestic machine and the tension was the same as a domestic machine and I had no problems with it. I loved quilting so much I upgraded to a HQ Fusion - and started having all kinds of tension problems. After several months of ungoing frustration and quilts with lots of tension problems I was really regretting what I'd done and felt I'd possibly wasted $10,000 (not a good feeling!)
There is a good ending to my story, I bought a towa gauge so I could make sure I had my bobbin tension correctly. I'd tried the drop tests and all that, and even bought a second bobbin case. Turns out I had two problems, some of my bobbins were bad and so I didn't get a good, even pull coming out of the bobbin, and the second was that I wasn't setting them correctly. Now I set them at 180 no matter what thread is in there - and then adjust the top tension.
The other thing I did was get a digital readout for my tension (you may not have that option) and know I have much better idea of where my tension is. I found I was often turning it the wrong way or not turning it enough.
I also discovered my new machine didn't like all the thread (Connecting thread's cotton) I'd bought that they Bailey loved. I do much better with poly thread, though now that I've got the other problems figured out I've only run into problems with Issacord embroidery thread (only thread I had backlash problems with). I use Maxi-lock most often, and the dealer that sold me the machine stocks it as he said it seems to be pretty universal that the HQ machines really like it and it's not expensive.
Though this does not pertain to a sit down machine as much, I also learned that my Bailey liked a tight quilt, and my Fushion likes a loose quilt, so I had to learn that difference too.
I love my Fushion now - and want to encourage others to just keep working at it and trying different things until you get it resolved.