It turns out familiarity was the most cited influence for reading a given book. In other words, the reader was familiar with the author. Somehow the reader knew about the author. They may have read another book by that author. They may be familiar with the author because he or she is already famous. Maybe they saw the author on television or heard her on the radio. The key ingredient was that they “knew” the author somehow.
Here is the breakdown of the percentage of people who ranked each option first in terms of how they influence when books they read / listen to:

• Familiarity with the author – 35.5%

• Read a synopsis – 25.8%

• Familiarity with the series – 17.2%

• Cover design – 6.9%

• Awards and bestseller stickers/badges – 6.5%

• Saw an ad for the book – 4.7%

• Author or celebrity endorsement – 3.1%

Read more about the study at Marketing Christian Books.