I'm not an expert on the subject, but I've been happy with the used musical instruments, amps, and speakers that I've bought over the years. I personally wouldn't consider buying a used television because the technology changes so quickly.
This is subjective because just as musicluvr opines, there are certain devices that are best bought as new. Over the years, people have tended to shun the refurbished items because of their shorter lifespan. I would buy a used item only if it was in a fairly good condition. You definitely have to conduct your due diligence.
The "return policy" is a very important fine print. If you like tinkering equipment, then better opt for refurbished gear for your experiments. I would rather save more for a new device if I don't want to worry about broken equipment.