One of the problems with this show (and with this episode in particular) is that most of the campaign slogans that Darren comes up with are an pathetic. And the slogan in this episode is absolutely dreadful. No amount of self-confidence would allow him to sell this poor excuse for a campaign to any discerning businessman.
So many of the plots from Bewitched revolve around the idea of Darrin (or Samantha) coming up with some brilliant advertising idea to save the day, but nine times out of ten, that idea is terrible - yet the audience is supposed to believe that it's brilliant.
The reality is that the show's writers simply weren't very good at coming up with slogans and advertising ideas. They were, after all, TV script writers, not advertising executives. They probably would've done better to farm out the creation of these slogans and campaigns to genuine advertising men who that knew how to write them.
