What should I look for in a quality down comforter?

I am looking for a nice king size down comforter. Every guide (on ebay) that tells me what is most important to look for is sponsered by someone that is selling down products. I'm looking for year round warmth, and it needs to be fluffy and comfy of course. What should I look for in a quality down comforter?

The only thing I know is that you should look for duck down, not one that's filled with feathers. A good one can be quite expensive but it will be worth it! There is no greater luxury or comfort.

look for duck feathers, they are good for breathing better