Craigslist has anti-spam software that blocks specific users to prevent them from abusing the website. Why does Craigslist block these users? It is typically a result of posting too many ads in a short time span or posting ads outside of your local markets. Craigslist typically tracks this activity by logging your IP address.
Aside from strictly following the rules, you could also use Craigslist posting software that ties in directly with the platform or use a proxy to hide your IP address. The platform route is much better for businesses. Using a proxy to hide your IP is grey area but can still work.