Is it permissible to listen to religious tapes before selling them?

There is no harm in listening to tapes before selling them. In fact, it might be necessary to ensure their quality and conformity to the buyer's specifications. However, if the intention is to use them and then sell them, this must be disclosed to the buyer if it is considered a defect that diminishes their value, due to the Prophet's (peace be upon him) saying: "A Muslim is the brother of a Muslim. It is not permissible for a Muslim who sells something to his brother, which contains a defect, not to disclose it to him."