Well he's the other director & family so trust is pretty crucial.
We chat beforehand, we both know what we need to be stocking, compare lists pre auction and discuss bits we disagree on. 95% of the time we think each other has made the right call. On the other 5% we try to prove each other wrong so it kinda just works.
Don't get me wrong, sometimes I go a bit strong on one through the door, sometimes he buys a dog, but that's always going to occur with hindsight.