In all likelihood you will sell only a few copies as no one actually knows that you have offered a book for free. It will also take a few weeks before the other distributors (Sony, Apple, Barnes & Noble, etc.), supplied by Smashwords, will change their price to 0.00$. One weakness of the internet is that the number of books on offer is huge and you are just a drop in an enormous ocean. Unless you learn how to tell people that your book is free, there is no way they will know. But you should not be talking all the time on social networks about your books and nothing else. The right way is to create a number of friends and acquaintances with whom you will communicate and tell them about your books only when you really need a promotion. Everyone will be glad of a free book and happy to help you by passing on the news about your book to their friends and acquaintances.