Is it permissible for a soldier tasked with selling cigarettes in a military store to increase the price of the goods and keep the difference for himself? Is this considered a consensual transaction? And is it permissible for him to sell gifts he receives from representatives and keep the money?

If working in the store entails selling tobacco or assisting in its sale in any way, then it is not permissible to work there, and one must leave it. However, if it is not possible to transfer to another department or find an alternative job, and there is a necessity to continue, then it is permissible only to the extent of that necessity, with the obligation to leave it immediately upon finding a lawful alternative.