Trade within the Imperium falls into two distinct categories: trade within sectors and trade between sectors. In general, the Imperium encourages trade within sectors, but trade between sectors is much more chancy. All trade within a sector is overseen by the sector's AI. While independent operators and commercial concerns actually haul the goods and trade, the trade AI keeps track of where all traders are within the sector, and has the authority to issue orders for traders to carry specific shipments in cases of "emergency" or "military necessity". Sector Governors rarely issue direct orders; rather, "suggestions" about "high profit items" and "Imperial favor" are enough to get traders where the Imperium, or to keep them away from somewhere the Imperium wants cut off.
Trade within sectors covers all items; everything from gems to foodstuffs travels within sectors. The short travel times and relatively low duties on bulk goods make such trips affordable, if not especially profitable. High-profit trips are more heavily taxed, but are still more profitable. Trade between sectors is mostly conducted in rare, high value merchandise; industrial use gems, rare metals, and luxury goods. This is where independent traders do most of their work However, the Imperium does not facilitate cross-sector trade as much as in-sector trade. A trader wishing to cross sector borders has to get the astrogation algorithms for a border world in the next sector, where customs inspections are conducted. There, he is given the algorithm for his destination. Destinations three or more sectors apart are very rare due to the time involved.
A word needs to be said here about Imperial blockades. When a world openly rebels against Imperial authority, the Stellar Guard imposes a strict blockade. Any craft approaching the planet are boarded and searched. Any craft wishing to even stay in the system must have a document issued by the Sector Governor, commonly referred to as "Imperial papers." These include a code segment that will verify the papers. If the papers are forgeries, the ship is immediately impounded and her crew arrested for forgery of Imperial documents and suspicion of treason. Often, notice of an Imperial blockade is enough to send ships running from the affected system, since Imperial blockades are notoriously efficient. Occasionally, small traders will try to run a blockade. However, unless their ship has extensive (and illegal) sensor stealthing, their chances are very slim.