freeports generally sell more common stuff - like the fury cannons of any power aswell as what other factions put up for sale there ( armor etc )
zoner bases ( gammu, primus, gran canaria, corfu, and that station in 49 next to gran canaria ) sell more exclusive stuff - like ships. gammu/primus are prolly an exception as they are flagged "zoner" but its said in the info card that they have been abandoned by zoners. - they are more no-mans-land, but slightly affiliated to zoners still, as they once were zoner bases. ( and hopefully will be claimed back at some time )