If you go with the notion of "I don't need to prove myself, I'm good enough - look at what I've made", then this is exactly how it should be. Otherwise you're still proving yourself and providing 2 weeks of your highly valuable time for free.

Those 2 weeks should determine whether it works out on other levels (e.g. are both parties comfortable with working each other) and if you do work in that time, you better charge for it.