title: PayPal IPN notify and success URL params
body: <p>I'm implementing a simple Buy Now button and I'm using IPN (not PDT) to verify the transaction.</p>
  
  <p>A thing that bugs me is that I don't understand how come only after I set the <code>notify_url</code> field to the button I also get the transaction variables to the success URL, as GET params. It would seem normal to be the other way around.</p>
  
  <p>Since the user could or could not choose to "return to the merchant's website" there's not way I should rely on that data. It does however seem to be identical to the one sent to the notify URL.</p>
  
  <p>Some clarification would help. Thanks!</p>