There are also many Windows 10 Pro and MS-Office licenses available from the grey market. All of my machines with MS-Office 2016 on them have this via grey market licenses, as does the computer on which I'm typing in regard to Windows 10 Pro.
There are things which need to be considered before going that route, but for many, it's one they will elect to take. Better that they take it after having given a number of factors their due consideration before doing so.
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On the Grey Market (for Software Licenses, specifically, but anything, really)
First, if you want to have as close to 100% certainty as is humanly possible that you are not in
any way engaged with any dishonest activity, even if it's
not your own, then do not purchase on the grey market. The moment you step outside of standard retail channels, be they brick and mortar stores, online stores, or direct from manufacturer online you have stepped out of the realm of certainty of everything being above board.
As soon as you decide you will purchase anything outside those channels, there is a degree of uncertainty involved. There are things that may give you a sense of how certain/uncertain you can be about the legitimacy of an item, but even those are never perfect indicators. If someone's offering something at 90% off, and has no long-term reputation, you should be reasonably certain that they're not legitimate. But, even then, there's a tiny chance they could be. Only you can decide where your line lies as far as avoiding engaging, even at distance, with dishonesty and what your obligation is to protect third parties that could be harmed because you might be purchasing something stolen or otherwise illegitimate. For most of us, we're not looking at 90% off and the nature of the seller's actions and motives are decidedly less clear.
When it comes to software licenses, my personal opinion, in this day of the ability to create nearly perfect counterfeit packaging, is that if I purchase other than through conventional retail channels I simply cannot have any way of knowing
with certainty as to whether something is real or counterfeit,
even if I do my due diligence. In the case of a software license, which is typically a sequence of numbers and letters on a card (at best) or sent to me via e-mail, I can have even less certainty. The only entity that can, and should, have that certainty is the one that issues licenses and verifies same before allowing use of their software.
My
ne plus ultra metric of the legitimacy of a license is whether the authorizing entity does authorize/verify/authenticate/activate when this is presented to them via the means they prescribe. If they do not know whether the license is valid or not, I certainly cannot be expected, as an end-user, to know that.
There are definite risks involved with grey market licenses. Whether those are acceptable to you is something only you can decide. The worst I have seen happen is that a license gets deactivated by the issuing entity after having initially been authenticated by them, sometimes leaving you with non-functional software, other times leaving you with functional, but unauthenticated and sometimes limited-functionality. You are faced with the loss of the money you spent for the license, and the time and money you will likely spend acquiring another license. You must decide if these are risks you want to face, and be aware that "the cheaper the price" compared to full retail the more likely they are to occur and the more likely the item is black market, not grey market.
Some references in regard to reselling software licenses and legal changes in the EU:
EU court rules resale of used software licenses is legal -- even online Computer World - July 3, 2012
EU Court Says, Yes, You Can Resell Your Software, Even If The Software Company Says You Can't Techdirt.com - July 3, 2012
Top EU court upholds right to resell downloaded software Ars Technica - July 3, 2012
European Court Confirms the Right to Resell Used Software Licenses -
Brodies.com - January 1, 2012
Can you resell software licenses? The latest legal position in 2016 The ITAM Review - October 31, 2016
A direct result of the above legal decisions has been the creation of both a cottage industry for small business computer recyclers and a major industry for large ones of selling recycled licenses. The former, while almost impossible to verify their honesty except through seller ratings from past customers, do exist as legitimate resellers. The latter, one example of which is
Relicense in the EU, are big businesses used by other businesses. It's almost impossible to question the legitimacy of companies such as these, as they'd have been put out of business by licensing entities if what they were doing was illegal. They're high-profile and high-dollar businesses.
The grey market should only be entered after you clearly understand all of the variables discussed above and have decided where your acceptable tolerance levels are for each, and for all of them in combination for any given transaction.
You now have the basic information you need to decide if you wish to enter the grey market at all, and how to assess the probability of whether something is actually grey market versus black market (which is definitely no longer grey). Proceed as your reason and conscience dictate.