No I think it discredits the content - think travel guides, and if its non fiction then it is driven by the sponsors and and and... 

I would rather pay for book rather than have someone pay for it and have the integrity of the content compromised.

Also if I want a free book we could always go to a lending library.

I am thinking about sponsored books.

The author gets payed by the advertiser(s) and this way, the book gets cheaper or even free for the customer.

For instance:

- Travel books and guides, technical books (marketing, photography, design, architecture, IT, etc) with relevant ads inside.

    example: A travel book with ads from an airline company, a local restaurant and a hotel.

- In online books you could find Sponsored Links relevant to the content.

The list could go on.

Well, it depends on the book and the ads. Would you explain more about both?