Is it permissible to sell items inside the mosque for charitable purposes, such as selling booklets and tapes, where the proceeds go to orphans and the poor?

It is not permissible to buy and sell inside mosques, whether it be for books or other items, even if the benefit accrues to orphans. The books can be placed in a special box with their price written on them, and a collection box can be placed nearby, so that anyone who wants a copy can take one after putting its price into the collection box, without bargaining or haggling.