Ok, so this would be something that can be enabled/disabled in the settings menu. All it is, is a basic check to see if x player already knows y recipie. If the statement is true, a prompt will pop up (say for lockbox opening, etc) asking if the player would like to purchase it anyways. Players will still be able to buy duplicate recipies so that they can sell/give to friends, and it will stop forgetful players from purchasing recipies they already know. Time and money saver c: