Umm. rotating banners, credibility?

[punisa]

Hello everyone,
I have a question that might be a bit silly... but here it goes.
We have a website with cca 50,000 pageviews per day and have decided (for the first time) to sell our advertising space directly to some companies.
I noticed that many sites use cost per impression (CPI) when selling ads.

So let's say company buys 100,000 impressions at our site. Okey, I put their banner up in the rotating banner space and track impressions via database. Once it's over 100,000 I simply switch it off.

BUT - how do they know that we are being honest about these numbers? What if (hypothetically) I take the banner down when it reaches only 50,000 impressions.

Should I thus build some sort of feedback page where they could (via user name and password) check their progress in real time? Or is this too much of a hassle that might turn off the advertisers?

OR - must you link a banner directly from their site and they track in that manner?

I apologize if these questions are completely noobish :)
Thanks.

[LifeinAsia]

All or any of the above. We've had some clients who just believed us. Others want us to pull the banner form their site each time (so they can track). Some want to be able to login and check stats.

[jamesfraser]

You could also have the ads served from an independent party. You might find a web design company that will build the ad hosting platform and certify the results for a small monthly fee. This may allow you to charge a higher rate as the results are certified.

[Luxoria]

If I was wanting to buy ad space like that I simply am unsure if I would trust the site itself to run the tracking data especially if the site is not well established for being an ad space site. (example, a site with only one banner spot)

As jamesfraser stated look into a third party to handle all that mess for you. projectwonderful.com is an example type of site that is easy to both sell and rent space.

Really, that's the easiest way and no need to spend time making new code and billing processes. The third party collects money from the renter and sends you money monthly. mmmmm did someone say cake?