Merchants of Halas Faction

[Cidz]

So I am attempting to finish the Mantel of Souls quest, and upon trying to get the Potion of Sorrows in Halas, I am KoS. I looked through the forums and online but I can't find any way to raise my faction with them to continue this quest.

Does anyone have any input on how to raise my faction with the Merchants of Halas and not ruin my heretics faction? I am at a lose on this one. I attempted to invis in and hand the money 500g over and then FD ... but almost died and did not receive the potion but still lost my 500g. Any info helps thanks !