Here are some tips I have learned..over the years shopping at Amazon... hope this helps...
The trick is, when buying from Amazon, buy from *Amazon*, make sure it ships from Amazon. When you check out make sure you select free shipping (if available), it defaults at standard shipping. If you notice you are ordering from another store through Amazon, then go to that stores website and check to see if they offer a better price or discounted shipping charge... sometimes they do...If not then buy from Amazon, it's probably safer...
Last if you ever have something in your cart and the price goes up, call and tell them, they will usually honor the price that it was when you put it in there as long as you call within a close time of the price increase.. Usually if they can't do anything else to help you they will try and give you a discount to your account that applies to the next order..If you have something in your cart and the price goes down, feel lucky.. If you buy something and the price goes down within 30 days call and they will give you a credit..
Oh and most importantly, try to call them during daytime hours for customer service issues like these, otherwise you will end up in the Philippians and they have little ability to give you these type of discounts and it will only frustrate you more.. Hope that helps...