I worked on several big Web sites for sewing machine vendors. They both sold a lot of refurbished machines for way under what the same machine cost new. In some cases, the refurbs came with a full manufacturer warranty and were refurbished by the manufacturer. These were typically machines that didn’t work properly right out of the box, were swapped out as warranty replacements, then sent back to factory technicians who first fixed whatever was wrong then carefully checked them out to see they performed up to specs before selling them as a refurb. The warranty on such items is usually either the full OEM warranty or nearly as good.
In other cases, some third party refurbishes things. They may or may not be trained by the original equipment manufacturer. The warranty is probably not as good, or is nonexistent. Here, test drive before buying.
Then there are charlatans who sell used goods as refurbished because they put a little polish on it to make it look like new again. Do a web search of refurbished material like you are buying and the reputation of the vendor you’re buying it from. Find out who did the refurbishing, what refurbishing means by their definition, and research the refurbisher as well.
Refurbs can be anywhere from a great deal on something that’s just as good as new to a complete ripoff. Caveat emptor.