Is an employee sinful who takes money from citizens despite his refusal, and gives it to the poor, for fear of embarrassment?

It is not permissible for an employee to accept a gift from someone who has business with their workplace unless the employers grant permission. This is based on the Prophet's (peace and blessings be upon him) saying: "Gifts to workers are unlawful gains (ghulul)." And in response to one to whom a gift was given while he was collecting sadaqa, the Prophet said: "Why did he not stay in the house of his father or the house of his mother and see whether he would be given a gift or not?" These gifts are considered akin to bribery and may cause the employee to prioritize the affairs of the one who gave the gift.