The reason you get ebay stuff in Amazon boxes, is because that's an Amazon box the seller already had from an Amazon order. I've got tons of empty Amazon boxes!
Amazon is a LOT more reliable than ebay. On November 19th, I bought something on ebay. The "seller" never shipped it. I had to wait until 12/10 to ask ebay to step in. They did give me a refund right away, once I could explain the issue, but that's 21 days of rattling around in circular weblink limbo. I knew he hadn't shipped it on day 3. Almost everything I order on Amazon is shipped for free the same day, and arrives in a day or two.
Generally a good rule of thumb for the larger sellers but please allow me to explain my own situation:
I am not a big record company but I do make a living selling a couple of different concert videos on the internet, through my own website and through eBay.
My own FAQ starts off with the disclaimer
"PLEASE ALLOW UP TO 30 DAYS FOR SHIPPING"
Now, it has never ever taken me anywhere near 30 days but I post that disclaimer because there are slow periods where I only get one order a day, or maybe two.
That would mean I am making daily trips to the PO. No thanks, cost of shipping envelopes and time to prepare is more than enough of a drain.
I wait till I have at least five or six orders, (or even ten) then ship them all out at the same time.
So it might take a week, or even two before I do ship.