This is assuming the user has clicked on a PPC keyword first and converted in the same session, if they haven’t you’re shit out of luck.
Because I don’t have the users’ cookie.
This, in my opinion, is a massive oversight on Googles part. I’m spending (well, I’m not, but a user with an AdWords account might) a lot of money to have my keywords shown and, unless my service is something you can purchase or convert online, I have no way of tracking the efficiency of those keywords. Fail Google, fail.
Google never explicitly says that I can’t do this, but they don’t explicitly say I can either. Searching for the answer on Google (or Bing, in case Google are cheekily hiding the info) turns up nada, except people bemoaning the fact that they also cannot do it.
One of the things I have found people talking about is PayPals IPN (Instant Payment Notification), basically, when a user purchases something via PayPal, when the money is actually debited from the users account, PayPal sends an event to an IPN URL, which is a page on your site, which, after confirming the call is from PayPal, can use a bunch of data to store the fact your user has paid on your own site. This is useful because often, people won’t click back to your site from PayPal once they’ve made the purchase, so, if you do something fancy on the confirmation page, you might lost up to 30% of your confirmation page visitors.
This is the page that Google want you to put your conversion code on. A page that may lost up to 30% of it’s traffic from leakage at PayPal.
Sucks right? Nothing you can do about it.
C’mon Google, give us an API or something we can poke conversions into AdWords with!