Trading in Account Sales means you can't sell Accounts with Recovery Questions, even if you don't know them, if you Buy or Sell an account with Recovery Questions, even if the player comes from RuneScape Discussion, they won't get banned, you should of not bought an account with Recovery Questions, the User who sold you the Account with Recovery Questions will have their thread locked, but it won't be worth the time.
So be safe - Buy with no Recovery Questions, if you're not sure before buying, you should see if they have pictures of the account before they're trading. If they have pictures, they're probably trustworthy, the 99% percent of time, they're most likely scammers.