How to tell if it's genuine?

I bought a Retail box of Windows 7 Pro for my wife's soon to be built pc.
The purchase was through Amazon and a company in Laguna Hills, Ca.
The price was decent and I've never had a problem with Amazon before so why not?
Got the package today in the mail and just opened it.
The upper edge of the blue Windows 7 cardboard sleeve is bent over and slightly separated. The shrink wrap is wrinkled in the same area.
Removing the plastic case from the cardboard holder I can see that the seal appears to be compromised.
There is a 'bar or line' which is part of the seal that is showing red except near the center, where it is silver.
Also, the squiggly line that runs the length of the seal along the words 'Win Pro 7 English US only DVD' seems to be slightly separated.
I've never dealt with anything like this before and could use some advice. Is there a way of using the numbers on that label to tell if this is genuine or should I try to get a new copy?
Thanks for any help.
H

You may find this link goes some way to answering your concerns.

Genuine Windows: frequently asked questions - Microsoft Windows

If the software is counterfeit it will fail Microsoft's validation checks.

Thanks for your help.
I was hoping to avoid opening the plastic case but I guess I've got to do it in order to check for authenticity.

Edit: It does seem to have been opened before I got to it but both discs are Holograms and include that beautiful word 'Genuine'.
And I do have a product key. Is there a link I could go to to verify that the key is new and valid?
Thanks.
H.

I don't think I'm expressing myself properly.
I'm not building the new pc at least for a few more weeks. If I find out then that there is a problem with the Windows 7 key, I'll be in a difficult position trying to get it corrected quickly.
I live on SSD payments and can't afford to just throw money away.
That's why I was hoping to find a site where I could check to make sure that this new key isn't already being used.
If there is no way of doing it then I'll just have to keep my fingers crossed.
Thanks for helping.
H.

I'm sure that Microsoft would be able to vouch for the software's authenticity if you call them and explain your worries.

I would have thought the Product Key alone should be sufficient as they should be able to verify whether it's genuine or not.

As for validation, that takes place after you've installed the software, which in your situation is not a lot of help to you. The main advantage of validation is that you get access to Microsoft goodies without having to go through Windows Updates first and you have the satisfaction of knowing your software is legal.

What is validation and how does it work? - Microsoft Windows