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The Manager setting "Restrict trade to other factions" purely relates to the station itself and it prevents the Manager from trading wares with ships belonging to other factions. You can use the global setting, or define settings for each individual ware the station may buy or sell. So you could have Globat Global set to NO and a couple set to YES, or the other way around (handy for stations with many potential wares).
If you assign ships to the Manager, this setting is not observed by those ship so they will trade between their station and other factions' stations. Two Your station may be in the same zone may trade with each other via their as one owned by a different faction. Intra-zone trade can take place via station cargolifters and in this respect, cargolifters operate like ships, ignoring the Manager setting.
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