The Wa FM supporters are a mixed group more akin to community groups (just like the residents opposing a highway in Sri Petaling), unestablished and of unknown potentials and capability.
Tom Riddle, who confided in no one and operated alone, might have been arrogant enough to assume that he, and only he, had penetrated the deepest mysteries of Hogwarts Castle.
However, by 1982 the Fenys family could no longer afford to maintain the castle, even though they received government support, and they put it on the market.
The good news is you've managed to locate the legendary dungeon containing the stash of ancient Stygian coins and the eccentric wizard who owns the castle has even generously agreed to let you have them.