Can the seller substitute another person to perform the contracted service when the buyer stipulates the seller's personal benefit/service in a sale contract?

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If the buyer stipulates the seller's service in the sold item, and the seller appoints someone to perform that work in his place, that is permissible. This is because the seller is situated as a commissioned worker (*ajir mushtarak*) in this scenario, who may perform the work personally or through a substitute. If the seller desires to offer monetary compensation (*'iwad*) instead of performing the service, the buyer is not obligated to accept it. Conversely, if the buyer desires to take compensation for that service, the seller is not obliged to provide an exchange, because mutual agreement governs compensation transactions, and no party can be compelled into one.