To be frank, your position is hurting you, and doesn't make much sense to me. If you supply customers with your source upon purchase, you're already working on

To be frank, your position is hurting you, and doesn't make much sense to me. If you supply customers with your source upon purchase, you're already working on a trust model -- without much effort, they could give copies to a thousand people who wouldn't have to pay. And if you're working on a trust model, you might as well give the benefit of the doubt to a paying customer asking for a refund.