Discount taxes for sell orders in 0.4 and lower systems. Perhaps introduce this as a skill that offers an additional 10% off taxed items per skill level. This would of course compound with other trade skills and standings.
Low sec trading hubs run by Pirate factions. Criminals can enter these systems through special gates guarded by pirate factions.
Aggression shouldn't be tolerated in those systems or at the gates into these systems, or else it won't work as trading hubs.
To prevent abuse: People with positive security standings and members of alliances may not enter.