When the profits of the consumer will increase, they purchase more goods and vice-versa. Hence, profits and demand have a directly proportional relationship. This means that the demand curve slopes upward from left to right. This holds within the case of superior or normal items best.However, this isn't the case with substandard items. Substandard goods are items of low price. Hence, while the earnings of the consumer will increase, he's going to avoid shopping for the substandard goods and shift to buying advanced or normal goods. So, the demand curve will slope downwards from left to right