The Good Manner KF94s on Amazon are pretty cheap and are a reputable brand. From what I recall reading on here, it's not very profitable to make counterfeit masks and copy all the branding and packaging for KF94s since the real things are so cheap. So while it's not impossible to get a counterfeit of a reputable brand of KF94, it's unlikely (though you might end up with gray market masks that were not intended for export for whatever reason.)