I think you asking about sponsor PSA's or purchase PSA's . There are many ways you can sponsoring affiliate such ads posting, Solo ads posting, Social Media Marketing, Through the Serach engine optimization of your own site about SFI and Pay per clicks ads. Otherwise you can purchase PSA's and purchase S-Builder Co-op. Sponsor PSA is very time consuming process you required lot of time but other hand purchase PSA's is not time consuming.
