From what I saw there are any number on Gumtree, with completely unknown provenance. I think you have to value both the spec and the provenance.
If the actual machine has the ports you want and is sound in battery etc, then the provenance is extremely valuable.
Just to add I looked for one for about three years. I ended up buying one from SC as the spec was superb and the provenance very strong. I'm delighted with it.