Nonsense. There is hardly a local government in Australia not hopelessly corrupted by local real estate interests. In many nations local corruption is endemic right down to every neighbourhood police station. Size isn't the question: money's corruption of power operates at all scales.

Size is absolutely the question. There is always corruption, but in small municipalities at least the scale of corruption is contained. In a sufficiently local area the corrupt has to brush shoulders with his unwilling benefactors and be shamed.

Empirically, that's plainly false. Corruption declines, on any level, when the right policies & incentives are in place.