That is not as easy as you think it is. IP address space is relatively cheap per IP address. But it is much more expensive per IP address prefix, which is how the filtering actually works.
Hence why these companies use VPNs to rent diverse IP address space.
Do they filter by prefix to stop geographic areas? I did block some Amazon scanning on an e commerce but taking down few ip's was enough to stop the waste of resources.
I tested about the VPN's and they just have updated lists of common VPN addresses. Using a custom VPN make them unable to filter so there shouldn't be any other sign that tells the server who's using the VPN. Perhaps a discrepancy about DNS servers use or some other leaks.
