Yes, it's next to impossible. I had put my book for 'free' promotion to try and get reviews, I had over 50 downloads but almost nobody bothered to review!

The only people that reviewed are people who told me that they liked my book, so I asked them to review it! All except for two, which were unexpected and came out from nowhere.

Sometimes you have to contact people who would like the book, and you might have to send them a free PDF copy so they are willing to review - but that review doesn't mean it will have a lot of value.