If you ever have cause to post a Poole-made loco, please, do not rely on the original vacuum-formed tray to protect the loco. They go brittle with age, and likely will not survive the post. Once the tray breaks, the loco has room to move in the box and it's this rattling around that causes the damage.
Below is a small selection of recent casualties. Sometimes the loco escapes damage, but the last image shows today's victim where all four buffer housings broke, as well as the bogie tower. In all the examples below, the external packing was undamaged. All very frustrating, as refunds do not stick broken parts back together.
My advice would be to pack the loco separately from the original box, well wrapped in something like bubble wrap, with everything then placed in a decent cardboard box. I usually message eBay sellers with this request, however to-date I have been ignored 100% of the time!
(https://www.ngaugeforum.co.uk/SMFN/gallery/155/9379-051125200810.jpeg)
(https://www.ngaugeforum.co.uk/SMFN/gallery/155/9379-051125200840.jpeg)
(https://www.ngaugeforum.co.uk/SMFN/gallery/155/9379-051125200907.jpeg)
(https://www.ngaugeforum.co.uk/SMFN/gallery/155/9379-051125200926.jpeg)
Yup I've had a few like that over the years, and not just Farish either. Old Arnold boxes used similar vac-formed trays.
I feel your pain. I have also told sellers to be careful with posting but to no avail. I once bought a mint class 37 only to have all 4 buffers smashed to pieces. And the seller thought I had made it up.
You can only try your best but sellers are in the main ignorant of this situation. Especially now that the packaging is so much better.
Bob
As a retired packaging engineer (!) I too have shipped n-gauge locos. It is obviously very important to ensure the loco cannot 'rattle' within it's packaging! Lots of tissue/bubble wrap/foam usually does the trick!