I'd say his first mistake was hiring the Jobblins 

Except hiring the Jobblins is never a mistake!

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Transcript:

Panel 1: The businessman practices his reaction to the robbery he staged, "Oh! No! Oh... No! Oh no! Hm, maybe an Oh? No! Ugh, how real do I need to sound so the guard won't waste my time with questions?"

Panel 2: Still practicing he starts to say, "Oh!"

Panel 3: Arriving at the door to his warehouse, he says an authentically concerned, "no."

Panel 4: City guard are rousing and leading the defeated thugs away as a captain of the guard is taking a statement from Abby and Erry. The captain looks up at the businessman as he arrives, "Ah, good timing," they say, "Actually, I have some questions about your timing, considering you called us before you got here, and reported a robbery that didn't happen."