Conditional Help

[MoMan]

I currently use this code to place a feedback link onto every post within my forum marketplace section:

PHP Code:

<if condition="!is_member_of($bbuserinfo, 1,3,4,8)">
<if condition="in_array($forum[forumid], array(24,36,37))">
<div class="info"><strong><a href="feedback_leave.php?u=$post[userid]">Leave Feedback</a></strong></div>
</if>
</if> 


I'd like to create a new link based on a few more conditionals that would allow the seller of an item to automatically move (to a predefined forum) and close his thread once he's sold the item.

I know that the code for this is quite simple, but how would I go about coding this to make sure it is secure so that it cannot be accessed in other forums or by users who did not start the thread?

If we assume the thread is being moved to forumid 50, what would the code to close it and move it be?

I know this is kinda complicated, but thanks in advance for your help!