The seller must disclose any faults in the item which may make it less desirable and reduce its price. There is abundant shar’i evidence to this effect. It was narrated that Wahb ibn ‘Aamir (may Allaah be pleased with him) said: I heard the Prophet (peace and blessings of Allaah be upon him) say: “The Muslim is the brother of (another) Muslim. It is not permissible for a Muslim to sell something to his brother in which there is a fault without disclosing it to him.” Narrated by Ahmad and Abu Dawood; classed as saheeh by al-Albaani in Irwa’ al-Ghaleel (1321).
And it was narrated from Abu Hurayrah (may Allaah have mercy on him) that the Prophet (peace and blessings of Allaah be upon him) passed by a man who was selling some foodstuff. He put his hand in it and found that it was wet. He said: “Whoever deceives us is not one of us.” Narrated by Muslim (101).
And Allaah knows best.