Is buying and selling in four shops located in a designated area on the basement level of a mosque considered permissible (halal) or forbidden (haram)? And is it considered selling within the mosque?

It is permissible to sell parts of the mosque for commercial shops if the endower (waqif) has specified that, because the condition set by the endower is binding as long as it does not involve anything forbidden. It is permissible to conduct transactions such as buying and selling in these shops, and the contracts are not considered to be taking place inside the mosque due to their separation from it.