This is clearly a pirate site. e.g. "A Brother's Price" is available for $7.99 at Amazon.com
, book by Penguin, "This price was set by the publisher".
This site is selling it for $3.99. Note that many of their books are at 0% off. My guess is that they have an Amazon account, and all books started off at 0%. When a book is bought, they buy it from Amazon, strip the DRM and send it to their "customer". Then they mark it down to 50% on site, and continue to "sell" their DRM-free version.
Almost certainly pirates and crooks. Don't fall for the scam. Do you really want to trust your credit card details to known crooks and fraudsters?