The premise of this episode is that Darrin believes Endora zapped money into the cab (which she didn't) and all the chaos that ensues afterwards. This whole scenario could have been avoided and rectified earlier when the cabbie realized that Kosko was the person who left the envelope in the cab. The cabbie drove Kosko back to Darrin's office building and they were waiting in the cab when Darrin came out. Kosko should have approached him then to get his money back. The cabbie would have confirmed that Kosko was his fare prior to Darrin and Larry, thus problem solved.