I used to own 10k IP addresses that I sold as proxy servers to internet marketers. I made about $20k a month and it paid my bills through college. I had no idea what I was doing and eventually shut down the company, but damn, I wish I at least kept control of those things. If you want to see some sketchy shit, look deeply into what the VPN companies are doing.
What are they doing?
When you “geolocate” an IP, you’re really just looking up the registered info for that IP’s ASN in the ARIN/RIPE database.