Windows 10: Sealed box version USB drive + activation code of Win 10 Pro sold online - legit?

A sealed box of Win 10 Pro is offered for sale on an online marketplace by a person with good reputation. There is little doubt that the box contains a legitimate copy of Win 10 Pro, and that the box is factory sealed.If I purchase that copy, do I obtain the license to use that copy of Win 10 Pro? Or not being the original purchaser from Microsoft not having the original receipt of purchase of Win 10 Pro directly from Microsoft confers no license on the end user? In other words, would a receipt of purchase from the online marketplace suffice to be the legit user of the Win 10 Pro?

:)

 

Recovery Drive Doubt

I created a recovery drive usb pendrive when i bought my laptop. That time it was Win 10 Home SL. Now i upgraded it to Win 10 Pro and activated it using "illegal software". So these are the doubts which i have :

1. Can the Recovery Drive reverts Pro to Home? (Recovery Drive was created during Win 10 Home SL. So if i boot Recovery Drive it should revert back to Home. These are my thoughts)
2. Will the digital license work after downgrading ?
3. Will there be any backlash ?

P.S. After upgrading it to Pro, there was a warning saying "digital license valid for Home SL, and not for Pro". I used an "illegal software" to activate it. Also i am a newbie so please explain it step by step.

 

Win 10 Pro OEM activation issue

Hello Larry,

Significant hardware changes such as replacing your hard drive or motherboard may lead to issues in activating Windows 10. To better assist you and provide you with the appropriate resolution, we would like to know a few more information. Kindly answer the
questions below:

• Did Windows 10 Pro came pre-installed with your computer?
• Do you have the Windows 10 Pro installation disc available?
• Are you getting any error messages when trying to key in your activation code?
• Were there any significant hard ware changes done on your computer?
• What were the exact troubleshooting steps you and the MS support teams have tried?

As an initial recommendation, you may check on this article and follow the steps provided to run the Activation troubleshooter:
Using the Activation troubleshooter.

We'll be waiting for your response.

 

Stuck at 0% when making USB OS installer for Win 10 / Also how to check if my prod key is legit?

- Stuck at 0% when making USB OS installer for Win 10 is this normal or is there something I need to do?

- Also how to check if my prod key is legit? I have a prod key for win 8.1 Pro complete with the installer (I purchased years ago) and upgraded to win 10 (free upgrade) then I notice that on the lower right part of my screen it's asking me for activation so
I tried but it keeps on giving me an Error Code: 0xC004F074

TIA!