They'd have varied goods, bit like less restricted equipment from Corvus Prime, but only limited amounts and higher price than from that pirate main base. if the NPC tradeship were to ran out of stuff to sale it'd have to go back for the station/capitol ship (if later added for more black market trading).
anyways, you could possibly also track the ships returning back for resupplying to discover hidden bases or big ships locations, what to do there? ummh, maybe do some high dangerous missions for chances of rare equipment, but it'd have check system that the player who'd complete these would be able to do these only once, until the equipment were to be lost, or, doable again after certain time had passed. anyway maybe too much specifics.. well here's some thoughts anyway from me. and my first post.

Good ideas, though there are pre existing topics about all of these things.

When I think of intergalactic wandering salesmen, I think of the Melnorme from Star Control 2.

http://www.classicgaming.com/starcontrol/sc2/aliens/melnorme.shtml

hehehe..... good times....