Why don't you sell PrepTests?
It saves you money.
Two related thoughts that guided us here:
1. We used to offer two versions of our course options: one with and one without PrepTests. In the former, we were acting as an intermediary shipper, which meant that students paid more for the same books than they would have if they'd bought them directly from a bookseller. A few of our students chose that option, but it always seemed inefficient to us when they did.
2. Only a few students chose for us to ship them books. The great majority bought them on their own, which told us how the market was moving. So, taking those students' lead, we decided to move everyone onto the less-expensive, more-efficient model of purchasing their books directly.
You'll find links to purchase the books of PrepTests covered in our course right here.