Instructions
The Basics
Collect all the beans once you get to Hogwarts so you can sell them to Fred and George to buy famous witches and wizards cards. You need those cards to unlock the duels later in the game.
Run over the beans that are scattered all over the hallway. Beans are also hidden in trunks, suits of armor, paintings, trophies and tapestries. Hit the beans with the flipendo spell to break them out of their hidden places.
Fly over Hogwarts once you've gotten your Nimbus 2000 and go through rings. A yellow ring is 1 bean, green is 2, red is 3 and blue is worth 10 beans.
100 Bean Bag
Find the trunk covered in slime on the third floor near the Defense Against the Dark Arts classroom behind one of the tapestries.
Use the diffendo spell to get behind the tapestry and then skurge to get the slime off the trunk.
Hit the trunk with flipendo and you will find a bean bag that can hold 100 beans at once instead of 50.
Hidden Beans on the Grounds
Visit Madam Hooch for your flying lessons. Before the tunnel that has three stars you will see some shrubberies.
Use flipendo on each one and they will spawn beans and other items for you to pick up. This can go on for a very long time.
Walk over to Madam Hooch when the beans stop falling out of the shrubs and back to the bushes and use flipendo again for even more beans. These beans do not go away. You can take as many beans as you can fit in your bean bag, go to Fred and George's shop, spend them and come back and do it all over again.
Hidden Unlimited Beans in the Confiscated Items Store Room
Finish the game but do not go into the Great Hall as you are told to do. Go outside to the grounds and walk through the tunnel in front of you. You will see a Gryffindor on the right. He will ask you to do a task for him. Accept his challenge.
Find out what he wants done and complete the challenge. He will send you to another person for another challenge. You will do this for six more people. The last person whose task you complete will give you a key to the confiscated items store room. He'll tell you how to find it.
Go to the store room, where you will see seven trunks. Six have wizard and witches cards and the one in the middle has a bag of 200 beans.