Dropshipping is similar to affiliate selling but you accept the customer's payment in your name and then the supplier mails the product to the customer. Basically you act as a middleman and make a little profit while doing it.

As for Public Domain books, being able to use it is the definition of the word. Basically anything printed before the Titanic sank is in the public domain. Actually, I think anything printed before 1924 is public domain. This means all of William Shakespeare, Charles Dickens, Mark Twain (to name a few) is in the public domain. You can make these available on your website as their complete text, sell copies of them and not have to worry about royalties to anyone. There are thousands of books both fiction and non-fiction that can be used for this. Being in Australia, you can probably use books detailing the voyages of the Pacific such as Charles Darwin, Sir Frances Drake and others to build content and then sell related items.

I know one guy who built a site about raising chickens based on a book written in the 1800s and sells copies of it on eBay.