1) Item is overpriced for what is being offered.
2) Seller stated that they have not checked whether the watch has been previously activated on cellular. That does not mean cellular cannot be activated. In the pictures, it simply means there is no current cellular service activated.
3) No box or charger
4) Used watch bought in bulk. History is not known
5) Not eligible for AppleCare+ etc
5) Too many red flags
I don't advise buying high end Apple products on eBay. Try the MR forum or possibly Swappa.