I don't know for this specific case, but here are some generals.
You need to stand outside of the sight of any Kill on Sight mobs, including the quest giver, but in such a place that you can be in range to open a trade window using 3rd person view. Once you have filled the trade window, have another player (in group) invis you and then complete the trade.
If you don't care about the faction hits it might be easier to find a high level enchanter to charm the mob for you.
This seems like a lot of effort for a level 11 though!
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