Yes, of course it's a scam. They don't have permission from the copyright holders to sell any of those books, and not a penny of any money you give them will end up with the authors.
Apart from the ridiculously low prices for mainstream books, the 'smoking gun' is the presence of the Harry Potter ebooks. Those are not available form anywhere except Pottermore.
Please don't give your money to crooks. If you're going to pirate ebooks, at least do it in a way that doesn't reward criminals.