refurbished or not

If you decide to buy from them make absolutely sure it was prepared according to the directions in this Apple document: What to do before you sell, give away, or trade in your Mac - Apple Support

However, I whole heartedly second rkaufmann87's recommendation of getting an Apple refurbished Mac. As he so aptly put it, there is no downside.

You would need to contact AppleCare to ask them once you have the SN. When Apple sells a refurbished Mac they change the serial number. AppleCare would be able to tell from the SN information whether it was new or an Apple refurbished machine. However, that ONLY applies if Apple refurbished the computer. If another reseller sold it as refurbished, that means it is refurbished by that firm and they DO NOT have the ability to change SN information.

My advice, pass on it completely and if you are attempting to purchase and don't have the money for a new one then buy from https://www.apple.com/shop/refurbished . If you do there is ZERO downside. These machines are identical to new, come with a new 1 year warranty, are eligible for AppleCare and can save hundreds of dollars ! If you don't see what you want, then shop often as inventory changes VERY VERY quickly.