i always put balls that can confuse him when i rack in the front. it is fair as he can do the same. if he doesnt then i get an advantage, also many times he doesnt say anything but it bothers him and causes him to not play as well.
i also always spot a solid with the number up so he doent have a reference point to aim at. or a stripe with all white where his aiming point will be. he can do the same as well. it is part of the psychological aspect of the game. it isnt cheating and may not be what someone else wants how the game is going to go.
I have seen some players, after knowing to which side his opponent will break to, place either the solid and the striped green balls or the solid and the striped blue balls as the top two balls in a one-pocket rack depending on the color of the cloth. This is apparently done to make it more difficult for the breaker to focus his aim at where the color of the two balls touch together on his opening shot.
I have also seen where some players will always purposely spot a solid with the number up on top. This is apparently done to obscure any aiming point for his opponent.
I know in either case its my opponent's hope that I break bad or miss the shot. In either case, when I see this, I immediately think one thought and only one thought,
THIS GUY IS A F***ING NIT!