amazon don't raise or drop prices unless you have the book at a different price at another big retailer like Sony, Kobo, Apple or Barnes & Noble.
Well, they do like to discount my books sometimes, but that shows as a discount rather than a price change. My books aren't normally on offer elsewhere. I think Amazon just like to discount me for some damn reason. The moment a book starts selling, amazon gets excited and takes a few percent off the top. I don't mind, as it's normally only a small amount. I put it down to them testing book sale methods and such. On the UK, they like to change my prices to round figures from time to time, like 49p rather than 71p, etc.
Prices will vary depending on what country you're in. I can purchase books from the US, but I get delivery charge and VAT added on top of them because I'm in the UK. I'm sure it's the same if you're in other countries that they have deals with for the Whispernet service.
check the other retail outlets you use and see what prices you have set there.
Felicity Heaton