Interesting.
In those years when we were EU, our UK car might have all sorts of (obviously “used” ) tools in the boot and we honestly explained they were for us renovating our maison-secondaire in France (which they were).
That seemed to satisfy the Douanes.
How times have changed… even for EU people 
From the start back in 1989 when OH came over in his truck with tools to do work on our house, he had to fill in and supply a Carnet for both UK and French customs to show what he had and their worth and what they were being used for. This then disappeared I think when every man and his dog began to arrive bringing even the kitchen sink but now with brexshite causing mayhem everywhere, it seems it has returned with a vengeance regarding paperwork and bringing stuff in whatever it may be.
The country was EU before Brexit, that’s why it was easier, the nationality of the traveller played no part in customs limits.
I wonder if an Owner might over-estimate the value of used-DIY stuff. The allowed Customs limit for FOC is surely sufficient if one correctly assumes that used tools etc have little value to a would-be Buyer, since the Owner will be unable to sell for a decent price until the tools are checked for safety/correct working etc… thus their value is small..
a bit garbled, but I’m sure you get my drift… 
Thanks for the link, I had been looking for that but couldn’t find it!