i couldn't give him the potion, until i realized why.

its simple.
the bargain and negotiation limit is 65.
if your char that speaks with marduk is lower skill than that, he will attack.

the way to overcome that is rise to high enough level with that skill, and also add rings, boots whatever helps that skill too.

hope that helps you guys.

I've managed to do it with hamlin level 8, with noble ring, and some blue boots.

Aaargh, so THIS is why I couldn't save the big malformed guy. I was playing "greedy but good" Rillow as long as this was possible, so I took all loot and rewards unless the questgiver was poor or in a miserable situation. My next run will be generous Dwarf no matter how self-contradictory that sounds.

Kudos!