Changing style for guests when AdSense potential gone

Based on data from AdSense-Analytics - I have reason to belive that most AdSense earnings stem from internet users searching for a specific topic in Google - entering postbit - sees the AdSense in the relevant thread - and clicks. And that is basically it. Besides this "first and last click" there is not much AdSense potential. AdSense for members is virtually zero and I am therefore not showing AdSense for members (I might add that I have a quite good CTR, but still I belive its only from "first page vists". Also there is a reason for this phenonemon, but I can always go into that later).

Basically what I would like is for guests to change style to member style based on conditions like, fx.:

- have viewed a low number of pages
- guest session time is like 10-20 seconds
- or something similar.

Simply not to scare guests away with ads, especially if I am not going to profint from them any further, besides what happens in the first pageview.

I have placed a notice on the index page saying that there are no ads for registered members. But still it would be nice to happen automatically. I know there is a mod on vbulletin.org that shows a style based on time of the day. So if I knew the conditions this mod could be easily modified I think.

So I need some input for a relevant "condition". If I had that I can modify above mentioned mod and post it here in this thread for other vbseo members to use.

I don't show adsense to members either. I've found all it does is lower CTR and eCPM. I show alternative CPM style and CPA style ads to members instead.

I simply use a template conditional in the style

<if condition="$show['member']">
<!-- member ads -->
<else />
<!-- guest ads -->
</if>