The 930's are a pretty rugged machine! Not sure if it has the serpentine stitch on the 931. There are a couple things to check on this machine before you buy it. It has a basing device built-in, and a needle-up clutch. Both of these can become frozen up when not used regularly. And not all sewing machine techs know how to un-gum them. There is a small amount of electronic circuit boards, but I've never seen one fail. It also may come with a rock-back foot control, that moves the needle up or down when you push with your heel. That's a great feature! They put criss-cross feed dogs in SOME of the 930 series. If you're going to use a walking foot with it, it won't feed very well with those feed dogs. The feed dogs that look like teeth feed better.
If it's in good shape, and you can get it for less than $400, you'd have a bargain of a machine that will last a very long time and sew an awesome stitch.