Civilian Shipping as a separate Quasi-line, once you develop better tech and old ships get scrapped, representing proliferation of shipping tech to smaller entities than the government and the big shipping conglomerates.
-Tramp freighters
Using older, obsolete engines, small cargo holds and a different logic in choosing destinations, going for the marginal routes. In systems with little military presence, they may try to smuggle (i. e. transferring their cargo without paying the dues)
-Yachts
Small, fast ships flitting from colony to colony, doing nothing much, but have to be protected
-Prospectors
Small Asteroid miners going for unclaimed asteroids with deposits <500 tons. Mined Materials may be bought (possibly via a starport?) or go into the civ economy, yielding a tiny amount of taxes
Independents
-Separatists/Terrorists
Spawned by high unrest. Ramshackle refitted small civ ships with semiobsolete weapons.
-Pirates
May plague underpatrolled systems. Build small asteroid outposts and small, crappy ships with semiobsolete weapons.
Wrecks
Should not be visible system-wide, but detectable normally by sensors