How did the Weasley twins in “Harry Potter” finance their store after dropping out of school?
The Harry Potter films understandably strip many details from the novels in order for the films to be possible. J.K. Rowling’s books are so complex and richly expressed that including every bit would never be financially or creatively possible. However, this naturally leads some storylines with limited explanation for those who only watch the films and haven’t read the books. The films have a tremendous continuity and flow to them, but there are occasional elements that happen inexplicably without the explanation provided in the books. For instance, the magical joke shop opened by Fred and George Weasley (James and Oliver Phelps).
The Weasleys are known as a relatively low-income family. The kids wear hand-me-down robes, Ron (Rupert Grint) is regularly chided by Draco (Tom Felton) for being poor, and the family has a large number of children which certainly contributes to their lack of disposable money.
At the end of Harry Potter and the Order of the Phoenix (2007), as the student body of Hogwarts is busy taking their O.W.L. standardized tests, Fred and George swoop through the Great Hall on broomsticks, ignite fireworks, and cause magical mischief before quitting school for good.
The next time we see the twins in Harry Potter and the Half-Blood Prince (2009), they are the proprietors of a massive magical joke shop in Diagon Alley, the wizarding shopping district. The films give no explanation of how this happened, it merely tells us that these two boys from a poor family, who quit school, quickly became owners of a huge retail establishment with a tremendous inventory that looks like the wizarding world’s version of Mr. Duncan’s Toy Chest in Home Alone 2 (1992).
For the background on this enterprise, one must consult the novels.
The Weasley twins have always been pranksters, and spoke often in-text about someday opening a magical joke shop. They are charismatic and born salesmen, and have an aptitude for creating magical tricks. These qualities are shown in the film through scenes like the aging potion they used in attempt to submit their names to the Goblet of Fire, but their discussion of the joke shop never really found its way into the script.
Nor did Harry’s (Daniel Radcliffe) guilt about winning the TriWizard Cup in The Goblet of Fire (2005) and its prize of 1,000 galleons. The films overlooked Harry’s distaste for the way he was assisted to victory in the TriWizard Tournament by the false Mad-Eye Moody (David Tennant). He wasn’t a winner, he was a pawn in a murder attempt that cost Cedric Diggory (Robert Pattinson) his life. Harry attempted to give his tournament winnings to the Diggory family but they refused, and Harry was left with what he felt to be dirty money.
During the Quidditch World Cup, the Weasley twins had bet all their money with a bookie named Ludo Bagman, who fails to make face in the films. The twins bet that Ireland would win the cup, but that Viktor Krum would catch the golden snitch. This turned out to be the result, and the two won a good sum. The catch is that Bagman paid them in Leprechaun gold, which is worthless.
Thus, it is Harry that gave the twins the money so they could fund their store. It is revealed very on in Harry’s story that he has a wealth of funds in a vault at Hogsmeade left over from his parents, so money is never an issue for him. Keeping the TriWizard Tournament prize money would only stand as a constant reminder of the friend he lost, and the way he was used by dark wizards. He happily turns it over to Fred and George so they can pursue their dreams, as it least then serves a noble purpose.