Google Display Network question

I'm very new to the AdWords game. I just signed up last week with a $100 voucher, so I'm experimenting a bit. I'm promoting my e-book, which is more than micro niche -- it's smaller-than-the-eye-can-see niche. However, the people I'm targeting will be highly motivated.

On to the GDN question: For the first few days of my campaign, I left the GDN settings to "Automatic Bidding" and got thousands of impressions and about 14-18 clicks per day -- almost all from GDN. I got zero sales.

So, I changed my strategy to put in higher bids for "keyword search" so I'm guaranteed first page (and in some #1 position) for the targeted search terms I know are related to my book. I then changed GDN to manual bidding and low-balled at $.80 bid, with a 50% increase for my target demo (middle-aged people).

My total impressions have dropped dramatically (182 so far today), but that's not surprising. I had one click at $.79 (obviously GDN).

I had one sale today, but I don't think it even came from adwords, as it happened well before I had that click. Organically, my top keyword target lands me on page 1.

So, am I being dumb in shunning the GDN? I get suspicious that some people are accidentally clicking on my ad or maybe even using click fraud. The ad clearly explains what the product is, and uses the word "buy" so people know it isn't free, so I can't imagine much "looky-loo" traffic.

Does anyone else with a highly targeted niche low-ball the GDN and focus on search? It will certainly let my campaign run longer.