I hate taking my machines and only do it if it the last resort. They like to touch things that are not broken. I took my brother in as I had bent something and said to only fix the problem. I requested that no tune up be performed. Of course when I went to pick it up the guy started in on all he did for the tune up. I just groaned. It never was the same after I got it back. It was like I had to break it in all over again. I would take them in for a little more tlc than I can give them if they would keep their paws off of stuff that doesn't need touching.
After watching my mom for years and a few consults with her I do most of my own work. It is harder now if you have a computerized one like most of mine seem to be.
While working at Wal-Mart, I used to help in the fabric dept sometimes when someone would bring their machine back for not working. Most of the time it was a tension problem or something else equally easy to fix. Sometimes it was a matter of educating the owner.