How to verify Original windows 8.1 key and product box yourself

Hi friends,

My laptop came with original windows 7, now its little more than a year old and have upgraded its RAM and planning to use it for 2 years or more. So, yesterday had problem in laptop and had to format it . I have formatted it previously and have used recovery disk came with laptop to restore system but this time it is not working and I think disks are damaged. So I am planning to buy new Windows 8.1 original DVD. I searched online and also in local shop, online its quite costly on reputed sites like snapdeal or flipkart or amazon.. one of local seller is selling original BOX of windows 8.1 for Rs. 4200 . Shall I buy it from this person, how can I verify it before making purchase because he says that he has got original package but if you opened it, then he will not take it back. But how can I verify it without opening and seeing the key ?

If anyone have experience then tell me how can I verify it myself ?

I think you can call customer care and verify its authenticity by giving box details over phone.