@zzt @soatok @CursedSilicon In cases like these, dang has already gone and done that work.
There's hints on these sorts of things: reused email addresses, lots of accounts registered at the same IP address or within the same ASN. You can't stop the abuse but you can curtail it. Machines are much faster than you.
Some situations are totally legitimate: MSFT, AMZN both route their employee traffic through the same ASN and rages as Azure/AWS respectively. My current company's VPN is built on Azure.
At each of these, when I visit Reddit, Wikipedia, and others, I get naughty check pages. I couldn't look at Digikey when I worked at Amazon from the office because of how many bots slam their site, I'd just get dozens of "we're just making sure you're not a robot"