I think you were nicer then I would have been. I don't like deception of any kind in any form especially when it comes to my money being given to someone else.
I order a lot of stuff from Amazon and Amazon vendors. I have many vendors offer free shipping and they will combine orders. Seems like a lot of vendors just take the easy way out and say Amazon won't let me when in fact it is up to them as it takes time to combine orders and still have separate invoices for Amazon for each order. If Amazon won't let them then how do many do it?