"I want to advertise and sell TripleClicks products...but which ones should I choose to promote?"
If you carefully browsed list of items at TC, you will find that downloadable items would be a better choice. E-books for example is easily downloaded to your email once you purchased them. The other option is to promote your local ECAs. Both will eliminate the shipping cost. Beyond that, high shipping costs might hinder you from getting your sign-ups or PRMs.