Ive been buying both new and used from Adorama, mostly, and B&H for over 15 years. I highly recommend either one. I have no data to support this but it seems as Adorama may ship a little faster. Ive never purchased anything from KEH (yet) but based on the reviews I've seen, including the ones on UHH, I wouldn't hesitate to buy from them either.
I seriously doubt age has anything to do with it. The old people who are grouchy and grumpy now were once young people who were grouchy and grumpy then.
This guy doesn't seem to know much about the Nikon D40. First of all, of course the D40 has a light meter. Then he said he had to manually focus the 18-55mm standard kit lens. The 18-55mm lens is an autofocus lens. Then he said he couldn't focus the manual 50mm. It's easy to focus with manual lenses. Turn the focus ring on the lens and look for the focus confirmation dot in the finder. Lastly, he said the D40 did not have auto ISO. It does.