title: Using payPal button - user can change the price before paying
body: <p>I have 3 items that I selling on my web site, I dont need to have shopping cart or stuff like that. After the user fill form with data, I navigate him to a new page, where I display all the data he entered, and the price. Now this PayPal button built from <code>hidden input field:</code></p>
  
  <pre><code>&lt;form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top"&gt;
  &lt;input type="hidden" name="cmd" value="_xclick"&gt;
  &lt;input type="hidden" name="business" value="test12344@gmail.com"&gt;
  &lt;input type="hidden" name="lc" value="EN"&gt;
  &lt;input type="hidden" name="item_name" value="aaa"&gt;
  &lt;input type="hidden" name="item_number" value="12345"&gt;
  &lt;input type="hidden" name="button_subtype" value="services"&gt;
  &lt;input type="hidden" name="no_note" value="0"&gt;
  &lt;input type="hidden" name="amount" value=""&gt;
  &lt;input type="hidden" name="bn" value=""&gt;
  &lt;input type="image" src="https://www.paypalobjects.com/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal"&gt;
  &lt;img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>With <code>JavaScript</code> I entering the parameters to the  new page,and setting price in the amount input (price) of PayPal button.</p>
  
  <p>As you click the button you navigate to a payPal page with the amount from:</p>
  
  <pre><code>&lt;input type="hidden" name="amount" value="199.50"&gt;
  </code></pre>
  
  <p>My question: Is it the right thing to do? any user, not even hacker can simply before pressing the button to change the amount and press
  the button...as a result he will pay (probably less) different price!</p>
  
  <p>I wanted to use the direct API, but it's only for businesses in USA, Canada.</p>
  
  <p>What is the best thing to do?</p>