News of the D810 and it's inherent problems.
Nikon ran into trouble with early versions of it's D810 camera, thermal noise being the issue that blighted images and caused considerable consternation amongst Photographers who shelled out good money for faulty goods. Below is the link to the Nikon website that will enable you to check your camera to see if it suffers from the thermal issue problem.
Beware of cameras being sold on eBay where sellers claim they are free of the thermal noise issue when they are not, if you do want to buy off eBay then make it a condition of purchase that the camera you intend to purchase is free of this problem and should it prove otherwise that the camera be returned to the seller at his or her expense for a full refund. There is also a scam where sellers will claim that the camera is in the UK but when it arrives it has been sent from Hong Kong, only to find a week later that a customs bill arrives and you are the Patsy for a seller swindle.
The second problem arises if you need a fix for this issue, if the camera is a grey import Nikon will not repair it under warranty even if it is brand new out of the box, you will be charged by Nikon for this repair. So many imports are sold on eBay with a bogus 3 year Warranty.