Is it permissible for a merchant to separate products that come in an offer (two pieces at a reduced price) and sell each piece individually at a higher price?

Contracts between manufacturing companies and their merchants at fixed prices constitute an agency, and an agent is not permitted to act in a manner that contravenes the condition set by his principal. If he does so, the contract is not permissible. However, if the seller purchases the goods and takes possession of them, he has complete freedom to dispose of them as he wishes.