Can I get a legal and genuine Windows 7 Ultimate copy from Ebay by buying a Retail Product Key?

I want Windows 7 Ultimate 64 Bit. I don't want an upgrade; it's for a new PC.

I see Keys for sale on Ebay, and can you get a legitimate version this way?

I see one item that say

GENUINE WINDOWS 7 ULTIMATE x64 Retail

It says:

new, never used Genuine
Windows 7 Retail product key and software.

A download link for the 64-bit operating systems will be given! Burn an unlimited
After payment is confirmed the key and software will be e-mailed to buyer's address.

System: Windows 7
Version: Ultimate
Type: Retail

100% legitimate and authentic
Not a trial [version]
Will pass WGA
key has never been issued to anyone else, nor has it been
previously activated. Key is not retrieved from Microsoft’s system until
buyer purchases key.

It's listed for $14.00USD, free shipping.

It's not the only ebay listing selling a key. How can they sell them so cheap?

I've gone to the site
www.windows7product-key.com

and it says only buy from a reputable dealer.

What I want to know, is what makes this so cheap?
1. It's some sort of counterfeiting?
2. It's something possibly stolen somehow?
3. It's a cracked edition somehow?