T.A. Uner
T.A. Uner asked Mark Phillips:

Mark as a fellow Author, let me ask you this: is the practice of giving away free ebooks in exchange for online reviews a winning, or losing strategy for Independent writers?

Mark Phillips I think it can be a winning strategy. The natural extrapolation of that strategy is making one of your books free for an extended period of time. This works especially well with the first book in a series.
I have found that making a book "perma free" for two to three months generates more reviews, more readers and more sales of your other books than giving it to twenty or so people for a review.
Perma free is basically the same strategy only expanded to a wider group of people.
Increased reviews leads to increased exposure and more sales of your other books as well as increased sales from your free book when you start charging for it again.
I'm not a technical guy and I don't understand the algorithms that people like Amazon use, but I do know there is quite a bit of evidence to support this strategy.
From my own experience, when I made my first book free, downloads skyrocketed and sales of my second book went up by a healthy margin as well.

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