Does the android marketplace use your merchant API callback url during the google checkout process for paid apps?

If I have a paid app on Android Market, will my merchant API callback url get hit when the customer goes to checkout? I am wondering how merchants / vendors / developers are protecting their Android marketplace apps.

I've used google validation before to implement custom integration, so I understand how it all works. What I don't see anywhere else that I have looked is what, if any, merchant / developer integration with the Android Market checkout process? I understand the market uses google checkout, but in this case the market is hosting the checkout process and not the merchant, so it's not clear if they are passing your url.

So where is the hook? Am I correct in assuming this is the merchant API callback url?