He actually explains the process
right on the front page:
...oooh, this is better than I remembered, because I thought he wanted people to send him Legal, Unmark, Non-consecutive CASH. See? He's better than Chris!
That said, he's not really realising how people buy books online these days. Today, I was looking for awesome summer reading and just bought the entire Harry Potter series as ebooks. Couldn't be easier. Found JK Rowling's webstore through Amazon. Paid 50€ via Paypal. Bam.
Downloading.
I also recently read an interesting article how people used these "cheque" things. Way back in the 1970s. Glad I've never once had to deal with that shit. Because we have electronic payments in this country.