Has anyone figured out Amazon advertising?

I've been trying to help a friend who wanted to try some paid advertising for her Kindle book. We've run three campaigns at a $5-10 a day budget, and haven't managed to spend a cent. I can't figure out where we went wrong.

I know I read that most people don't manage to spend the whole $5/day, so I wasn't expecting to do that. But I find it odd we haven't managed to spend ANYTHING, although the campaign shows active and delivering.

I've gone in and played with the settings. Even had the placement for top of search and product pages up to 700% at one point. Then it just emailed her "out of budget." So, since we've spent NOTHING so far, I suggested we raise the budget to $10. Still spent nothing.

We also used the default bid and dynamic bids, where it raises them up and down. Weirdly, each campaign shows exactly 99 impressions and 0 clicks. That seems...odd? I know we must be doing something wrong, but have no idea what.