Our supply of post-it notes was running low, so our Inventory Department ordered a packet of 5 from eBay. They arrived in two days, delivered by Amazon, and designated as a gift. At first, we were totally at sea as to what happened. But a little research on The Google unraveled the conundrum: Certain eBay sellers actually drop ship through Amazon. They have Prime Amazon accounts or place order that are big enough which gets them free and fast shipping (indeed, where the eBay seller is noted as "private" and provides "fast shipping," it likely is a drop shipper. Here's the caveat: Because the eBay seller is making a profit, you might check Amazon before buying from eBay because you likely will find it at a lower cost (unless the eBay seller bought out the entire supply (our Inventory Department went to eBay because it could not find the post-it notes it wanted (we use only blue) on Amazon).
PS: If you have an Amazon Prime account, and live in a place that has an Amazon fulfillment center (which Phoenix does), then if you opt for delayed shipping in exchange for a future discount, you most likely will still get the order delivered within 2--4 days by one of those nice new little Amazon delivery vans.