What is the ruling on the action of a merchant who always sells his goods at the highest price, whether that is due to a high purchase price or the prevailing market price?

Trade is intended for profit, and there is no limit to it. What is forbidden is lying and deception. The price is determined by the mutual consent of the buyer and seller, as Allah Almighty says: "But [only] an exchange by mutual consent from you," and the Prophet said: "Indeed, selling is by mutual consent." Gentleness, tolerance, and sincere advice are among the characteristics of the people of faith.