All of the marketplace rules are available here.
Selling Facebook Pages and performing Link Exchanges do not violate the rules here.
In fact, you may have stumbled upon the Links section:
Links - Net Builders - "Buy, sell, and trade links."
Infractions are also very rare. If you follow common sense, you'll never have a problem here.
However, I advise you to refrain from threads that insult other communities. Those usually never end well.