How can you tell if your PS4 is brand new or refurbished?

I recently bought what was advertised as a brand new PS4 on eBay from a small tech company. A few days after purchasing it, two different reviews on the PS4 that the company sold them were posted. They both claimed that the PS4 was not factory sealed like promised i the ad and that it might be a refurbish. I was just wondering if there is a way to check whether a PS4 is brand new or used/refurbished. If so, how do you do it? Would the serial number be of any use? Should I just call customer service and see if they can check?

Refurbished isn't necessarily a bad thing, but if they're selling it as brand new, that's bullshit. Contact the seller