What is the ruling on a cow breeder increasing the price of milk for his regular and new customers in the month of Ramadan, and is it permissible for him to differentiate in price between the two categories?

It is permissible for a Muslim to sell his goods at the price he desires, as long as the sale is by mutual consent, due to the generality of the Almighty's saying: (But Allah has permitted trade and forbidden interest) and His saying: (unless it be trade by mutual consent). However, a Muslim merchant should adorn himself with noble character and be lenient in his buying and selling, taking into account people's circumstances and conditions, especially during Ramadan (definition), so that he may be included in the supplication of the Prophet, peace and blessings be upon him: "May Allah have mercy on a man who is lenient when he sells, and when he buys."