The problem with paid posting is you will have to offer better rates if you want quality posters. However, when you are offering better rates, it might cost you financially. When you offer low pay rates, you can get posters only form low-tier countries where they use English as a second language. Most people who use English as a second language make low-quality posts on forums.They are required to innovate not repeating the same threads again and again as this will affect bad the SEO. Some kinds of discussions are reopened every day or every week like for example how to earn X amount of money from PTP sites and doesn't add any value to the reader or the forum.