Cybercriminals stole $15 million from a U.S. company by inserting themselves in email correspondence relating to legitimate business fund transfers. The tactic is called Business Email Compromise (BEC) and is one of the most financially damaging online crimes according to the FBI. BEC is a lucrative scam because we rely on email to conduct financial business transactions, such as wire transfers.
A casual sales process can get you started as a one- or two-manshop. Beyond that, you need more formal processes to scale.