I can't argue with Don K.'s advice although I would suggest there is another approach with Best Buy.
It all depends on whether this camera was on the recall list (how to find out is elsewhere on this site). Let's assume that 2014 camera was not recalled. But when you get your "newer" replacement version it was. Then you have to deal with a new issue.
Seems to me you could wait awhile and use whatever Best Buy has as a no-questions-asked return policy, let's assume 90 days. Use the 90 days to test the camera further. If you want to return it then, do so. If the camera works the way you expected it to work, why go through the hassle?
I suppose the definition of "new" also needs to be considered. Unless Best Buy knew something was fishy, I believe they thought they were selling you a "new" camera. Unless someone can say a 2017 version of a D750 is "better" than a 2014 version it would be OK to have one, wouldn't it. If you want to really push on this and the camera is one you are willing to keep...tell them unless they give you a discount (some money back) you want another one. Many ways to consider here. Good luck.