We use Esellerate for payment.

Note that you will only get a license number.
The application is the same as the demo!

To get your demo to the full version, enter the license number into the "registration" window. (file->register)

As the license number is case sensitive and the application will quit if you make a mistake, it's best to use copy/paste to enter it in the "registration" window.

As most of the programs undergo constant changes, it's very well possible that every now and then there will be a newer version. You can install that and use the same number, unless the version number goes up by a whole point (e.g. 1.8.2 to 2.0)