MC is a complete idiot.
1) He should have kept the negotiations going and extracted as much gold as he could from that lady. She got a god involved so it does not make sense that it would be easy to cancel the negotiations if the MC insists on it continuing. And the god also seems to say he can continue.
There's no need to find out who stole his stuff from that lady. Just get lots of gold and stuff to help complete his mission and the rest can be stuff like she and her group are bound to not start any hostile action against him. Doesn't have to be in one lump sum payment either.
It's unlikely she's 100% innocent either, so if he wants revenge just get the revenge through making her pay.
2) Getting rid of all his guns = really really stupid.