[uxp]

> You can also limit exposure by blocking messages based on user IPs.

Craigslist already does this to an extent in their high volume categories. For example, one cannot post Job Listings in highly populated areas (like New York or San Francisco) unless the posting IP address comes from a place near there, and the account is verified via a phone call. Anyone not fitting this description must pay a certain amount of money.

The other side of the coin is the blackmarket selling of Phone Verified Craigslist accounts along with proxy lists in those same markets which can effectively bypass any IP filtering put in place.