Is the sale described here considered unlawful or impermissible, bearing in mind that the questioner is prepared to return the money if the sale is not lawful?

What the questioner did was to conclude an agency contract, the basic principle of which is voluntary work. Therefore, it is not permissible to take payment unless the man gives it of his own accord as a gift.

Scholars differed on the validity of an unknown gift: The Hanafis, Shafi'is, and Hanbalis held that uncertainty (gharar) prevents the validity of a gift. The Malikis held that uncertainty does not affect the validity of a gift, and this is the most preponderant opinion due to the strength of its evidence.

However, if custom dictates that agency is for a fee, then the fee must be specified in advance. Otherwise, the questioner is entitled to a customary wage (ajr al-mithl). If it becomes clear that what the questioner took in excess of the actual price is the customary wage, then there is no harm. If it is more, the excess must be returned. If it is less, he has the right to demand it. And if the additional battery or bag was a gift with the camera, the questioner has no right to sell it to the man, and he must return its price to him.