When you check the shutter count of your new K-3 (II) don't be alarmed if it shows a few shots since they may trigger them at the factory before packaging them. 2, 5, or 6 is normal for a brand new camera. If it's over 10 I might be slightly suspicious, but for a 'used' camera that was returned I would expect the previous owner to have taken at least 25-50 shots just trying it out, so it would be obvious if it was used.
My K-3 was purchased used with 20,000 shots already, and I'm now over 30,000 with no issues, so I wouldn't be worried about looking at a used one on '
the Bay' or the
Pentax Marketplace if you're interested in saving a few bucks. You can find some good deals on a used K-3 now that some people have upgraded to the K-3 II.