Someone with more experience will hopefully chime in here, but you might try making a mod that removes the Sound references for each trader in the sounds.xml, I'm new to modding, but it looks to me like each trader has their own set of sound files referenced.
for trader jen the greeting it look like the line is:
<SoundDataNode name="trader_jenlikefirstgreet"> <AudioSource name="Sounds/AudioSource_VO"/>
<Noise ID="1" noise="7" time="3" muffled_when_crouched="0.5"/>
<AudioClip ClipName="Sounds/VO/Trader/Jen/trader_jen_firstgreet_01"/>
<AudioClip ClipName="Sounds/VO/Trader/Jen/trader_jen_firstgreet_02"/>
<AudioClip ClipName="Sounds/VO/Trader/Jen/trader_jen_firstgreet_03"/>
<LocalCrouchVolumeScale value="1.0"/> <CrouchNoiseScale value="0.5"/> <NoiseScale value="1"/> <MaxVoices value="10"/> <MaxRepeatRate value="1.111"/> </SoundDataNode>
I think that if you made a mod with the line:
<remove xpath="/sounds/SoundDataNode[starts-with(@name='trader_jenlikefirstgreet')]" /> in it's sounds.xml might be what you need to remove that sound, but to be honest, I'm new to modding so I could be wrong and I have no idea what the effect of removing the sounds would be. but if I'm correct, you would just need to duplicate it for the other trader sounds you want removed.
If I can tomorrow, I will try to test it and see. If no one else has replied by then I will let you know what I find.