Options > Controls > "Use Double Click or Single Click to Select Object and take Default Action" needs to be set to "Single Click" or "Single Click Except Attack Dblclick"
If that is set as single click, then one click should be doing things like targeting and hailing at the same time (for NPCs). This behavior is (to my knowledge) not controlled by the UI whatsoever. If that setting is correct and you're still not hailing an NPC on a single click then report it to SOE via /bug.
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