I put three comic volumes and a bag of skittles (making sure it added up to at least $35) in my cart and Amazon says i'm eligible for free shipping, but when I proceed to checkout, there is no free shipping option and it says it will cost me $13 to ship.
I've tried replacing the bag of skittles with another comic volume and it still counts shipping despite my cart saying I was eligible. I don't really know how to check amazon facilities.
Another possibility is that, as I recall, these are all "eligible" for free shipping, but when you go to the checkout a 2-day or other shipping method is selected by default. You have to click the "free shipping" option in that section to get the slower, but free, delivery.
Anything that is not eligible for free shipping would cause charges to be added, the skittles too were shipped from Amazon facilities?
Some items are add on so they don't count for the $35 if all items are regular choose 5-8 day shipping.
Did everything ship from the same facility? If not that is why you did not get the free shipping