It appears that their retailer is taking a page out of the "Book of the Month Club" scam. For those of you who are too young to remember; The Book of the Month Club would mail you a book that was yours too keep. If you did not want that book, all you had to do to avoid being invoiced was to put it back in the box, tape it up to USPS requirements, walk it down to the Post Office and mail it back within a few days.
The usual come-on was to have a few top drawer books as window dressing and then vast numbers of third tier books.
Many third-tier books were lost in the shuffle and never made it back to the post office within the required time window. The customer ended up paying full retail price for books that could be had at the bargain barn and flea market for one fifth of list price.
The purchase agreement
I had to type this out by hand. For some reason, the vendor disabled my mouse so I am unable to copy-and-paste. I could not even take a screen print. Your speculation regarding the motives for making it very difficult to reproduce this boiler-plate is as valid as mine.
By clicking on the submit button I would authorize Digital River authority to make charges against my credit card into perpetuity. I would also be giving Digital River the right to transfer that authority to unknown parties. The only way I could shrug off the burden would be by following some, undisclosed, chain of links.