From Indies Unlimited:
[I]f you have books listed for sale on Amazon.com and you’re not taking advantage of their Author Central platform, you’re shooting yourself in the feet. No, not the foot: both feet. Repeatedly.
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I’ll show you how to merge your books. I heard that grumble. Yes, you need to merge your books. Here’s why.
What the hell is merging books? Well, even if you claim your books to Author Central, you may have multiple versions or what they refer to as editions: Kindle, paperback, hardcover, audio, etc. If you merge these, they will show up under one title heading, and the shopper will be able to see every type of edition available in one place. That benefit is huge – that way you can provide ONE link to a book and people won’t have to search for their preferred format. The other awesome thing about merging your books – is let’s say your eBook has one review, your paperback has three reviews, and your hardcover has two. Once you merge those editions, ALL the reviews will show for each – so instead of people seeing one review for the eBook, they’ll see five. That’s much better, isn’t it? I knew you’d see it my way.
Link to the rest at Indies Unlimited