Good advice Graham - but I hate the way they see this choice as a last resort for those who can’t afford to buy new. I always try to buy tech (and lots of other things) secondhand even though affording new would be no problem, because reusing and recycling is the ethical, environmental choice - and really ought to be everybody’s first choice.
But if everyone did that there would be no decent secondhand stuff 
Make provision for wiping the HDD/SDD and installing a fresh version of Windows.
Well - my point was that there’s something wrong with the perception and presentation of repair, reuse and recycling as second-best - when in fact we should do those first, and buy new only as a last resort.
I wonder if you saw the recent comments by the head of the UK Environment Agecy to the Association of British Insurers…
“Much higher sea levels will take out most of the world’s cities, displace millions, and make much of the rest of our land surface uninhabitable or unusable,. Much more extreme weather will kill more people through drought, flooding, wildfires and heatwaves than most wars have.
“The net effects will collapse ecosystems, slash crop yields, take out the infrastructure that our civilisation depends on, and destroy the basis of the modern economy and modern society.
“If [this] sounds like science fiction let me tell you something you need to know. This is that over the last few years the reasonable worst case for several of the flood incidents the Environment Agency has responded to has actually happened,"
Like Geoff Cox, I tend to buy used tech. I do this because I often get a better piece of kit than I would if I spent the same money on a new one. Or I get a piece of kit I want but can’t afford new.
For laptops I have had excellent devices and first class service from Rapid IT Store | eBay Stores. They recycle business/corporate machines - l/tops/printers, all sorts. The laptop that is my ‘desktop replacement’ is a military spec build HP. Core i5
To do the biz once I’d bolted for FR from ES with just a cabin bag size suitcase, I bought a Toshiba Satellite Pro C50 15.6" Laptop Intel Core i3 HDMI USB 3.0 8GB 240GB SSD. : £154.99. inc F.O.C next day delivery. Came with a fresh load of W10, as all their laptops do.
For quite a few, health was the issue. One of my very elderly bertholders went unconsious out at sea. His terrified wife managed to get the boat back to the yard. We hauled it out and stuck a For Sale sign on it.
Others, esp in the realm of tech, are addictied to upgradeitis. This must be the only way the mob phone industry survives in any volume now.
Or the device they bought is beyond their capabilities to use or use often enough to justify the outlay. This is particularly the case with cameras and musical instruments/recording tech.
As a pro photographer I have never bought a new camera or lens. The Nikon D600 I bought was ‘new other’. It had never been registered with Nikon, so I got 2 years g’tee. I saved about £500.
I’ve flogged all the Nikon full frame stuff - the issue for me was weight - and the used Micro 4/3 camera and lenses I bought to replace it are all pristine, indidtigushable from new at 3/4 or 1/2 the new prices The camera body came in its original box and even has 12 months warrenty on it.
The trick is to zero in on the target object which represents a problem to the owner for issues other than condition/function. Whatever it is, that is out there.