What is to be done when fatwas from scholars contradict each other regarding matters such as banks and stocks, and is it permissible to adopt the fatwa that allows it while informing others about it, and does sin result from that?

A Muslim who is not knowledgeable in Allah's Shari'ah should ask those among the people of knowledge whose scholarship and piety he trusts about what is unclear to him, and act upon their fatwa. His responsibility is thus discharged, for Allah Almighty says: "So ask the people of the message if you do not know." He may ask them for their evidence to put his heart at ease. And righteousness is that which the soul feels at ease with and the heart feels at peace with.