Pretty much what Saab said.....
Plus....
Download only with activation key
Hmm.... due to COA requirements, its unlikely OEM would be available download only due to the affix requirement (except perhaps to the large manufacturers who, I believe have the option of a BIOS level COA embed). If they're claiming to flog a retail copy at those prices I'd be even more suspect....
As for the rest.....
There is a difference between being able to buy it and being able to do so legitimately.
In the vast majority of cases, the average end-user will not qualify, as per :
If you are building a system for your personal use or installing an additional operating system in a virtual machine, you will need to purchase Windows 8 software or a Microsoft retail version of Windows 8.1 software. Windows 7 and Windows 8.1 system builder software does not permit personal use, and is intended only for preinstallation on customer systems that will be sold to end users.
There is a reason OEM is so cheap, that is because of its restrictive licensing terms.
In the long term, retail copies are a better bet as the licensing terms are more generous in various areas.
As for buying software off the bay' .... well...
