The rules of the darknet market include no drugs, no child pornography, no counterfeit currency, and using traveler's checks and super bills to avoid detection. They relied on Secret Service to avoid law enforcement and always checked their logins before going to their drop address.
The three main rules for a successful Dark Net Marketplace are avoiding counterfeit currency, not selling drugs or buying them, and refusing to facilitate the sale of child pornography.
Brett tells the story of the scam he used to order computer parts through Outpost.com and the various steps involved in making sure the scam worked properly.