Yes, concealing a defect is deception (ghishsh) and unlawful, and the Prophet said the one who deceives is not of us. The Prophet also taught that buyer and seller have the option to rescind as long as they have not parted, and that if they are truthful and make everything clear their transaction will be blessed, but if they lie and conceal, the blessing is wiped out. Therefore a Muslim must openly point out any fault in his merchandise; a sale made by hiding a known defect is sinful, and the buyer who later discovers it has the right to return the item or seek compensation (khiyar al-ʿayb). Honest disclosure, even when it costs a sale, is a source of barakah.
Evidence — the daleel
Sahih al-Bukhari 2079 ṢaḥīḥSahih Muslim 102 Ṣaḥīḥ
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Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.