Anyway....I discovered a neat little way to find out how many people are actually searching for keywords on Amazon. All you do is find a listing where customers can tag an item, and directly underneath is a field labeled "your tags". Input your keyword and Amazon will autofill and suggest related keywords. (kind of like it does in the the main search bar....only with numbers of searches)
Here is a screenshot of what I mean:
I'm not sure if these numbers reflect monthly, yearly, or weekly usages. But they at least will give you a good idea if the particular keyword you want to use is in demand or not.
I used this method for awhile with success, and wondered why none of the Kindle courses I had taken mentioned it. Then, when I signed up for Kindling (not an affiliate link...though I wish it was because this is the best Kindle course I've ever taken), and Geoff Shaw mentioned it, I knew it was spot on!
I don't cut out the Google Keyword Tool altogether though. When I find a keyword that seems promising on Amazon, I always double check it with the Google Keyword Tool, and if it seems promising there as well, I use it.
Hope this helps!