I've had Graham Mackinlay do work for me on a couple of guns purchased at auction and couldn't have been more pleased. You could certainly trust him to give you an honest appraisal of a gun for sale. Visited his gunroom last year and concluded that much of the really quality stuff that passes through the hands of reputable dealers sells before it gets listed on the web, so if you know what you want get the word out there but don't expect a bargain for a top quality gun.
Dave