It is always necessary for you to understand the perspective of the customers. Customers feel really happy when they are able to get the kind of the stuffs that they need which include the free products like the copies of some publication or something relevant to the content that is present in the book. It is also good for you to sell the kindle eBook of yours for free so that you get so many customers for your book. If you decide the cost of your eBook as something really high and then sell that as a free then it can really make the customers choose your book as they may think that they are getting better discount than any other kind of the eBook. There are less chances for your eBook to come with so many things compared to others but the eBook that has got higher cost and when it is sold in much lesser price then it would obviously make the customers feel happy and choose that what you need.