In the post link below, David Kudler explains various reason to go the free route and various reasons not to. As with most things, it really depends on what works for you at this moment in time. He also explains how to get Amazon to set your book for free, even though they don’t want to. But I wouldn’t go to that effort unless you’re going with perma-free. If you want free on Amazon and you’re not part of their Select program – just do an Amazon giveaway.
Personally, I think the perma-free thing only works if you have A LOT of good reviews for the first book in a book series before you even set it at FREE. (How much is A LOT? – not sure there is a magic number. How many reviews would it take you to pick up a book from an author you didn’t know?)
There are so many ways for readers to get books for free now a days, a free book from a completely unknown (and unread – if you don’t have many reviews) does very little to make a shopper click that button and pick up your book.
That is not to say free for a week or free for a day or book giveaways aren’t a good thing. I think short-term giveaways associated with some other promotion you might be doing aimed at readers you know is a good idea. You do want to get more reviews. But keep in mind, just because you give a book away doesn’t mean you’ll get a review. I’ve given away a lot of books on Amazon and Goodreads and the Fussy Librarian but gotten very few reviews from those. Hopefully I’ve gotten a new reader or two. And it only takes one or two people who read your book to decide they like you and will tell others about you and your book to help get your name out there.
What you can do is set the price for the first book in a series (or a first book in a collection of books you have) at a lower price than the rest. If someone really wants to try your book, $.99 or $1.99 or maybe $2.99 isn’t going to stop them.
And remember, pricing also depends on the length of the book and the genre your book is in. So check out what other unknown authors are charging in your genre to help you decide what to do.