Roleigh, I've had good results from an inexpensive Brother machine that I purchased about 18 months ago. If it has problems, it is always a sign to me that I have thread tension set wrong, cheap thread, or a super thin fabric that I haven't figured out yet. Some velcro has adhesive on the back, and that can gum up your needle if you aren't careful.
The problem with purchasing a used machine is that it might have been given up because it had problems, and without servicing, it might continue to have problems. In other words, you don't know whose headaches you are inheriting.