Speaking in general terms, the people who would be looking for a self-help book on any particular topic would not be trolling a free site looking to download freebies. The non-fiction market, in particular the DIY/Self-Help market, does NOT work by the same rules as fiction.
1. People looking for help are not "going to take a chance" on a new author just because a book is free. They are looking for someone with expertise in the field who can help them.
2. People who are buying self-help/DIY expect to pay for that expertise. If I need a book on how to talk to my teenager about drugs, I want to get a book from a source I can validate and trust. Not Jane Doe the Self-Published Author I never heard of but her book is only 99 cents. I'm going to be happy to drop real money on a book by someone who has credentials I can be comfortable with. Those credentials will be different depending on the topic. But they will be far more important than price.
3. Self Help books are not impulse buys. If I am browsing throught the freebies and see a free book on How to Raise a baby hedgehog, I'm not buying it because I don't own a baby hedgehog. If, however, a month later I end up the proud owner of a baby hedgehog, I'm going to be looking for a book. At which point, I'm not trolling the freebies. I'm doing a search on "how to raise a baby hedgehog"
Your ad dollars would be better spent on websites that cater to the people who would be specifically looking for the self help book.
