Is a Muslim who does not trust the Mufti of the Palestinian Territories obliged to inquire until certain of the religious ruling, or is he bound by his fatwa?

Regarding administrative fees for loans, it is permissible to charge them within the limits of actual expenses. Any increase beyond that is considered forbidden usury (riba). This is what the Islamic Fiqh Academy has decided, and it is the fatwa (religious edict) that is issued. A Muslim must seek what is lawful and inquire from those knowledgeable about what is unclear to him. His conscience is not cleared except by asking someone whose knowledge and piety he trusts, and he must follow the one he believes to be the most knowledgeable and most pious, not what aligns with his desires.