Things have changed. It makes more sense to outsource warehouseing and fulfillment to people who do that for a living. So I'm turning over our online operations to Amazon. Yes, buy our books at Amazon.
Click here to buy our printed books on Amazon.
We experimented with electronic-only books for several years, and interestingly enough, people still wanted the printed versions. Thus, we don't have much call for individual e-books any longer, and so it doesn't make sense to maintain a server and associated credit card processing for the occasional one-off.
If you absolutely, positively need just an ebook, you can order the old-fashioned way by downloading a paper order form (.DOC file) here, filling it in and sending it to books /at/ hentzenwerke.com after zipping it up.
Payment? No, we don't take PayPal (they're still EVIL), our ebook-only customers have had good success with using an Amazon gift card. Use this 'books /at/ hentzenwerke.com' email address.