FWIW, from Midsouth's FAQ page:
What is that extra charge or credit on my card?
At the time your order is placed (emphasis added) we retrieve only enough money from your credit card to initially cover the merchandise and the "estimated shipping cost" which is computer generated. Only when the items are pulled from the shelf, put in a box with packing protection and wrapped, the actual shipping weight is known. At that time the order is invoiced, and depending whether the estimate was high or low, we either issue a credit or seek the additional funds. Please note that the estimated shipping cost might become inaccurate if the order contains big items that need to be shipped in multiple boxes. If in doubt, please give us a call and our friendly phone staff will be happy to assist you with any questions.
I have only ordered from Midsouth 3 times, and they all shipped the same day, so credit card charges weren't a problem. The quoted policy may only apply to in-stock items. They may waive it for out of stock items, I don't know. I will continue to order from them unless and until they charge my card and don't deliver. I really don't see that happening, though. They are great to deal with. ymmv