I rarely see nice ones bring more than $300. Make sure the foam donuts are good, those are a particular PITA to redo. And that the ferrofluid has not dried out and ruined the highs. And that they have a properly functioning KUBE, without which they will not work properly.
I love Kef but the 103/3, which I used to sell when new, have turned out to be a lot of trouble.