If you want to go down a rabbit hole of shady proxies run on compromised/trojaned end user SOHO routers or PCs, google "residential proxies for sale"
It's amazing how easy and comparatively cheap it is to get access to thousands of residential IPs. Is it via spyware running on people's machines? Shady people working at ISPs doing nefarious things for cash? We never knew....
The key thing to know is that if you want your traffic to come from an IP "in" some other country (according to geolocation databases anyway) it's really only a few bucks a month to get a proxy. Most of them have poor IP reputation so they suck to use on Google, but work very well for everything else out there...
Might be as simple as https://hola.org/ & https://luminati.io/ - "unblock a website, download our VPN client", meaning you "unblock" by using somebody else's line. And the also sell access at luminati. Most users aren't aware of the implications.
a) The type of "services" luckylion mentions where people have opted in to a shady gray market thing reselling proxies through their connection.
b) compromised home routers/gateway devices/internet of shit devices
c) compromised home PCs (mostly windows 7/10 trojans/botnets)
Hello ALL social network folks who don’t know how spam was the Origin of social networks. (Fb, Friendster, hi5, blah blah blah)
Who the hell is documenting the history of the internet
Step 2) Hammer Zillow with all known ip addresses
Step 3) Profit