Walmart does sell MiBoxes (or they did 1 month ago). If you have a sales person who is unfamiliar with the product or does not have the correct sku they will not find it and tell you that walmart had never had the product. (Source: this happened to me before i finally showed the guy the recipet from a week prior and he was able to find the correct sku and found the 1 they had in inventory.
look on the silver plate on bottom of device. It should read mdz-16-ab or mdz-22-ab. These identify Xiaomi MiBox official international models with legit Google AndroidTV opeating system.
Any different model is designed for China domestic market
I don't believe there are any fake xiaomi mi boxes out there, they are already pretty cheap, what are your concerns?