I believe this seller(alldayzip) 靠谱. He has good rating and I bought
iPhone 6S from him before. In my case, it's truly brand new(unopened box)
with full 1 year Apple warranty.
According to the following link, model A1660 is sim-free version. You might
do more research to confirm. http://www.redmondpie.com/sim-free-unlocked-us-iphone-7-and-iphone-7-plus-now-available/
It would make even better deal if you have 8% eBay Bucks.