In the episode where they are trying to keep it from Maurice that Darrin is mortal, it looks like he could have figured it out from the start, I mean the house that Samantha was living in, and he knew that Darrin WORKED for a living b/c they said he was out of town on business, so wouldn't he know from the start something was wrong?

Then again, they all worked good and hard to convice Maurice that Darrin was a witch.

I think Maurice assumed Darrin was a warlock who liked to work.