The only "factory refurbished" official source is through Apple.com.
Anybody else is more of a recycler selling used MacBooks going through whatever unofficial "refurbishing" process they do. Unlike Apple, most of those don't replace the battery and probably have a very limited warranty (whereas Apple treats their own factory refurbished essentially as new with a full warranty, ability to purchase extended AppleCare+ coverage, and has a new battery and new serial number).
The company you are looking at may be totally fine (or not), but it's important to realize they are doing they own thing and probably aren't any sort of official Apple seller. Just look at the fine print very carefully and evaluate if you trust them to buy a used Mac from and to stand by it for any "warranty" they offer. Since it's not Apple-factory refurbished the real Apple warranty would have expired years ago and any warranty you get would be strictly through that company.
I would research the company by name to see if you can find message boards or forums where people talk about their good or bad experiences with that company. Personally, at a minimum I search for: <company name> scam, and also look for Archive.org captures of their website to verify they have been in business for at least several years.
