How to track conversion in Adwords, from third party sites

If you are getting a return callback from the third party site upon purchase success, then ask them to piggyback some "success" parameter if they dont already do so. You can then use that parameter to the call adwords conversion script.

Dan's quite right -- if you place the Adwords conversion tracking code on your thank you page, it should record the conversions correctly. A lot of sites have this arrangement where a third party site handles the transaction, then return users to the original site's thank you page. I've set up tracking in exactly this way on a hotel site (where the booking is processed by a booking engine on a separate domain.) Bear in mind that if you're also using Google Analytics to track how users behave, you'll need to modify your code slightly and have the third party site install your tracking code on relevant pages on their domain.

Google can not monitor how much time you were on site. It can only deduct the time you were on one page to another to find the time on page. That means, when you leave a page to 3rd party site, and then come back to your site for confirmation, in perspective of your site Google Analytics will treat you as if you never left it. But, the cart dropout or people not visiting the success page to your site can not be tracked. Many 3rd party sites uses parameter URLs that has certain parameters from which you can identify the actions preformed on the 3rd party site. You can use the AdWords conversion code in the "Thank You" or "Success" page. Better if you have different "Thank You" or "Success" page for PPC. But, for goal setup, define the last page before going to 3rd party site as "Required Step" and then use the "Thank You" or "Success" page as last step.

Exclude the 3rd party site as a referral or the conversions will appear with the source being referral rather that the original advertisement. Yes, if you set up landing page as conversion it will track it, but they all will be attributed to "referral" from the 3rd party source rather than attributed to the ACTUAL source (like a specific PPC ad group etc.). So go under admin in Analytics, then select property, then "tracking info" then exclude the 3rd party domain.

If the only way that a user can reach your thank you page is via the off-site payment page, it sounds like you can put the tracking code on your page. This would be almost the same as having it on the payment page (there may be a small number of lost hand-offs but it shouldn't be enough to worry about).