BARAS (rice) & Akad

Baras (rice) is the staple food of most South East Asian communities. Thus it is a commodity that can be traded between a seller and a buyer. In Islam, a transaction (akad) is carried out between them with the item sold i.e. rice. I think it's okay if you buy 1 kg of rice at $1.50 and sell it at $1.80 with a profit of 30 cents. It's not stealing or taking advantage because it's different from usury. If for example you want to buy 1 kg of rice for $1.50 but then you don't have cash, so you go to a creditor to borrow $1.50. But then you pay 30 cents extra to the creditor the money you owe. Then that extra charge is haram in Islam because you are taking advantage on someone's difficulty. So there is a big difference between usury (loan/borrowing) and profit (selling/buying). There is an ikhtiar (effort/work) in the transaction but not in the other one because it is exploiting other peoples' energy to acquire for personal benefit which is very bad as it can generate hatreds between two parties.