Expecting unique client machine/network profiles for each seller account seems fundamentally incompatible with a web-based access model. Then again, maybe it's merely incompatible with a Good web-based access model.

Modest proposal: Distribute smart cards and readers to sellers, and use mutual-auth TLS for everything. Or offer this as an option to anyone willing to pay $xxx for their initial sign-up fee.

> Distribute smart cards and readers to sellers

Jeebus, this makes too much sense.

If Blizzard can hand out OTP generators for it's users, surely Amazon or retailers can do the same for it's sellers.

Hell, look to Google and their Authenticator app or SMS-based 2-step login (out of band auth channel would be better).

This already happens on college campuses. I've seen IP bans on websites take down access to every student in the dorms because of their NAT setup.

To see how easy is to identify your computer, go to the EFF site: https://panopticlick.eff.org/

Why would you want that? It seems like both Amazon and the user come out ahead. Anyway you could just use a whitelist for cookies and set your user-agent string to something really generic.

Like the Google Search Bot. That's always fun (and strangely unlocks a lot of sites).