Is it permissible for a person to claim knowledge of the unseen, such as sorcery, or to forbid something permissible, and how should visitors be received in a designated place of worship in exchange for money?

The sign of a wali (saint/friend of God) is faith and piety. A wali's claim to know people's ailments and reveal certain matters is not necessary; rather, most who make such claims are awliya' (friends) of devils. The prophets themselves could not know everything except through revelation from Allah. Therefore, one who sits awaiting people and informs them of their afflictions, it is feared that he has a connection with the jinn or sorcerers. Thus, it is advised to stay away from such individuals. If a person suspects himself of sorcery, he can treat himself with legal ruqyah (exorcism/incantation), either by performing it on himself or by seeking it from someone whose righteousness and uprightness he trusts. Entering the mosque is permissible for Muslims, disobedient individuals, and disbelievers, though there is a difference of opinion regarding thebeliever's entry.