What type of postbit template are you using?
postbit_legacy template is like what we use here, where the member info sits on the left side of the postbit.
postbit template is like the one you see on
www.vbulletin.com/forum, where the userinfo is above the message body.
Make sure you added the html to the right template, also where exactly did you place this line of code?
HTML Code:
<if condition="$post['userid']"><div>Trader Rating: (<a href="traderratings.php?$session[sessionurl]u=$post[userid]">$post[ratetradetotal]</a>)</div></if>