Earlier quoted context omitted.
>In the end Amazon has banned the two sellers, but moving forward it is difficult to police 3,000 listings so we have not been expanding what we are doing on there. Does the API still return offer count? If you're truly the only legit seller, set up an alert if offerCount >> 1. Even without the API this should be pretty trivial to scrape.
But the first sale doctrine means there can be other legit sellers. There's no way to be certain whether a third party seller is selling a counterfeit (except by buying it).
> first sale doctrine means there can be other legit sellers
This is not necessarily true on Amazon.
There are larger brands that make deals with Amazon, preventing their products from being sold as new by anyone but themselves. Other people can sell it, but it must be listed as used. An end-run around first sale, but that's the way it is.