The mere fact a product key is legitimate - even when confirmed as such by MS (which you'll only be able to do after purchasing it) - does not guarantee the legitimacy of the sale, for the reasons I outlined.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Ok your probably right about what you stated.

After messaging the seller about the validity of the Microsoft Licensing with the eBay seller I receive a reply.

These are acquired from my husbands work-place he works with the Microsoft partnership program, this is how we are able to offer you this great item at a great price, otherwise you would have paid a lot more at large retail stores like Staples or Office Depot. Please note: Often times a live chat Microsoft representative will says things to persuade you to purchase additional or new softwares from them or they simply just do not know.

So I don't really know One Hundred percent about the Microsoft Office 2016 legitimacy as I'm taking the sellers word about it.

In business and then private world requires a certain amount of trust. If you're not able to trust anyone then one may likely end up as a failure.

But I guess your right there's really no way to determine one hundred percent the legitimacy of software.

I think perhaps to become closer to one hundred percent "known" legitimacy would to purchase directly from Microsoft or a Microsoft Certified Reseller, who potentially could sell you some software (with or without their knowledge) that is stolen.