Is it permissible to take the excess amount when returning an item to a different store for a higher price, knowing that the item was purchased for a lower price?

It is not permissible to take the price of the commodity or the excess amount unless the owner of the shop agrees and is aware of the true situation, because goods are returned only to the shop from which they were purchased. You must consult the shop owner and repent to Allah, for the Prophet, peace and blessings be upon him, said: "He who cheats is not of me," and "The property of a Muslim is not lawful except with his consent."