First, my suggestion was more an attempt to simplify the "how do I keep an eye on 3,000 listings" process. Second,
> 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.