Do you have something to show? An example text + the corresponding code would be ideal, so one can estimate whether it's worth to buy your package.
Binaries show nothing, everybody believes you that you can program simple examples with SFML and Box2D. But since you offer
to teach other people, it would be good to check the quality of your tutorials and your code. Of course you do not have to show all of them, but one lession would be nice. Just that everybody is able to have a first impression...
By the way, you shouldn't be so closed about your project. You cannot advertise your product with two sentences that contain almost no information, you have to convince people of paying money for your product. Because as soon as something costs money, people have high expectations