Is there a specific limit for profit in Sharia, and is it true that the maximum profit is one-third?

There is no limit to profit beyond which it becomes unlawful, nor is it restricted to a third or a half. However, a merchant should be lenient in their dealings, based on the Prophet's (peace be upon him) saying: "May Allah have mercy upon a man who is lenient when he sells, when he buys, and when he demands his due."