The first advantage to purchasing a used sewing machine is clearly the savings. The second reason is that many new machines offer bells and whistles that you are likely to never use. They may be cool features, but may not be worth the added expense based upon your intended use. Buying a used machine can offer you a selection of machines that offer a useful selection of bells and whistles, but ones that are more practical for everyday use.
The three main features that I look for are ease of threading, sturdiness, and the number of stitches featured. If you are new at this, having a machine that is easy to thread is very important, as this is something that you will have to do often. The thread will break on even the most accomplished seamstress. Sometimes, the needle will too! And to complicate things, a machine that is improperly threaded will exacerbate the problem, causing the thread to break even more, or to create weak stitches that will have to be removed. Threading should be simple enough that the seller can easily show you how to do it in less than one minute.
Sturdiness is a very important factor. A “feather-weight” machine sounds appealing, but it also means that many of the internal parts are not metal or may be electronic. This means that your machine will require regular maintenance and professional repair. A machine that is primarily constructed of metal parts that you can actually maintain yourself is a practical choice. And the more metal parts, to include the base of the machine, the better. You will find this feature in older sewing machines. My favorites are the Singer machines that were made in the 1970’s.
If you are a beginner, straight stitches, a zig-zag stitch dial, and a button hole setting is very important. These are the basic stitches required to accomplish almost any task. Some specialty stitches that combine the zig-zag stitch with a straight stitch are nice as well, and are very common, but not necessary if you are just beginning. A more advanced seamstress might use that stitch feature occasionally, but very few patterns call for it. Stick to the basics because it ultimately means less maintenance. The basic stitches will be clearly labeled on the front of the machine with easy to use dials.
As far as choosing an actual brand, I would not recommend making that a priority. Most recognizable name brand manufacturers of sewing machines have been around forever. They all make good machines and have different things to offer for the novice to the advanced. If you stick to the criterion above, brand will matter less. If you get caught up on name brands, then you are likely being “sold” on features specific to that brand. Any good sewing machine will have the basic features that you will require, so just focus on ease of threading, sturdiness, and the number of basic stitches that are pictured on the machine and you will be amazed at how quickly you learn how to sew!