EBay plays whack-a-mole with these so you’ll rarely find lots of feedback. I must have bought over 50 this way now (it’s my default way of getting office). I just get a feeling from the way the main bulk of the ad is written setting out the steps and the one I linked to fits that style (it’s probably the same seller all the time).
It goes like this: ebay or email message from seller. Go to setup.office.com and put in the key. MS works out what version it is and you choose the language and download – you’ll need an MS account for this.
Install office, try online activation and it will almost certainly fail. Use the phone activation and you’ll probably be asked how many times this key has been used, answer zero (probably why the online fails). MS reads out the installation key (make a copy of it to use if you need to reinstall) and off you go.
You may get a link to use a web based authenticator which TBH is a bit of a faff but then so is the phone activation. But I tend to use this even if it’s not in the instructions as it’s quicker. I’ve tried using old keys and totally made up ones in the app and it gets you nowhere, so I am pretty sure it’s just another semi-official method. Whatever, I’ve not had any issues once activated.
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