"- Err, we have no money. - Sigh. ok. Go and attack our rivals over there."

Strictly speaking, this is not what happened, and a gross oversimplification. The Byzantines were not exactly rivals of the Venetians. The whole thing was quite bizarre in fact, Roger Crowley has a pretty good story of the events leading up to this in "City of Fortune: How Venice Won and Lost a Naval Empire" if I'm not mistaken.