For example, the player could make a potion , but such hand-made stuffs's quality should not match the ones from the mage guild . The guild is professional and they make potions systematically, which means their product's quality would be the best in the game , the second place are the ones sell in common stores . As for the player's hand-made potion, could be in the third place. The expert of alchemy may make better potions , but would never match the guild's product. It's quite simple , the guild own a whole produce system while the player just have his hands.
Not just potions, any stuffs could be made by player , such like weapons, armors, if they exit in game, should follow such rule.
Any thought about that?