A knocking radiator is one complaint shared by a whole line of apartments
Steam heat and prewar risers produce failures that repeat vertically through a building, so one clip is useful to a great many people at once.
A banging radiator, a main vent that stopped venting, a top floor that never gets warm while the second floor cooks. In a steam building those are not separate problems, and a super hears about all of them in the same week.
Film the fix plainly. The valve, the vent, the pitch of the radiator, the noise before and the quiet after. A clip that cures a knock somebody has lived with for years buys more goodwill than anything you could pay for.
Aim it at building staff. A super in Astoria or Riverdale watches something useful and remembers where it came from the next time a managing agent asks him for a name.
Ductless work in a brownstone is the other set worth owning. Line hides, condensate routing, where an outdoor unit can practically sit on a rear facade. Owners search for exactly that and land on sales pages instead of answers.