title: Preventing referral scams
body: <p>How can you prevent "referral scams"?</p>
  
  <p>For example, in a wordpress-based site of mine, I suddenly noticed that someone clicked a link from some site I had never heard of. When I followed the link, there was obviously not a link to MY site. The site was selling products, in this case books. All comments followed a similar speech pattern, and the website URL for each owner of these "comments" was the amazon.com link to the product.</p>
  
  <p>Obviously a scam, I quickly backed off the website.</p>
  
  <p>Is there any way to prevent these forged referrals via PHP?</p>
  
  <p>Some way of telling if they are automated or do not come from a reputable source?</p>