It probably wouldn't work all that well, or it would require a complexity that would make it too cumbersome for most. First, what percentage of the materials were gathered in the US from mining, farming, etc? What percentage makes the product "American"? What if no materials came from here, but manufacturing was performed here? Or manufacturing wasn't, but final assembly was? Or none of that was, but Americans were employed packaging it here? Or transport provided jobs for American freight and parcel haulers? What if an entertainment product such as a movie or album was made in the US, but packaged elsewhere?
Globalism makes it all tricky. You could probably make a site with only 100% American everything - but then don't expect to have a broad selection of products, and be ready to watch people buy elsewhere on price, because people say they care a lot more than they actually do when it's their wallet.