Unfortunately, this is no biggie.
I have gotten equipment that is used from nearly any dealer, both physical stores and the big name "reputable" online merchants. Even from Amazon.com.
1,500 actuations is basically new for all purposes, although it really offends one's psyche that they didn't get to take the very first photo with the camera.
Think of it this way: how is a company supposed to offer customer service if they don't do this? If they have to throw away any camera that someone returns, they would go out of business. If they relegated it to a shelf that said "scratch and dent" they would lose $500 and never be able to sell it for a long time, perhaps losing $1,500 in the end. If on the other hand, they properly inspect it and have approval from Canon to continue offering the original warranty, then no one loses.
I just bought a "brand new" camera from Best Buy the other day which was obviously used. No tape around the battery, etc., and little flakes of dirt and kleenex which had been used to try to clean the camera up. But I paid for the two-year protection plan, and so if it makes the camera go bad more quickly, then it's all good for me. If it becomes unrepairable before the end of the warranty, then I can have it replaced with brand new "equivalent technology." But the lens was clean, and it was obviously inspected by Canon because some of the items were sealed. So I just trusted Canon, known for its excellent customer service; and my protection plan was my ace in the hole.
I completely disagree with all you say. First of all, sure, the companies need to make money, but they also need to be honest. They need to tell you that it was used, and maybe give you $50 off or some other incentive. That should be included in their overhead.
I also disagree, I don't think 1,500 actuations are "like new". Given the short time the camera has been out, his 5DIII was used quite a bit apparently.
The fact that you knowingly buy a camera at new price even though it was obviously used is odd too. On top of that, you happily spend the money for extra warranty rather than asking Best Buy to give you a free extra warranty since they are obviously selling you a used camera. You might as well take the chance and buy it from Amazon for less. I just don't understand your logic, however it is very kind of you to support your local dealer and letting them get away with bad business practice. Some sales clerk is probably very happy and will probably be encouraged to try to do this again...