Determine If Windows 7 Product Key is OEM Before Installation

I have some Windows 7 disks and product keys that I bought on eBay. They didn't come in a box, but the disk and the product key sticker otherwise look legit. What I want to know is if the keys are OEM or retail, before I use them. Note that this was not answered by this question because in that case he had already installed and activated the key.

Solution 1:

A somewhat weird solution, but it works. Windows 7 has a tool to download the ISO file, but only for retail versions. That means if you enter an OEM key, it will say that your key is invalid because it is OEM. If you enter the key and it is successfull, that means it is retail.

https://www.microsoft.com/en-us/software-download/windows7