I would also be a bit upset, but it sounds like you'll end up with the new machine you thought you paid for. You're lucky they could still find you an 870 - the 875's been out for awhile now. I bought the Sapphire 830 last year - it was a display model I got for $899. I had no problem registering it. I don't understand why such a difference in the pricing of the new 875, they don't have that much additional on them to justify such a hefty pricetag. I remember when I bought mine how she said the new models would be a bit more expensive, at her store, they were about $400 more than the previous year's models.
I don't care for the staff at the Viking inside the Joann's near me. They are not very friendly, even when you buy things from them. I go out of my way to go to a different dealer who is very helpful and friendly to me.
Good luck with your new machine. I just love mine!