Assalamu Alaikum,If someone is repairing mobile phones and selling them and when they repair the back of the phone a bit of the waterproof capability is lost . Does this person need to include it in the phone description for resale and if they don't is their income haraam?JazakAllah.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Any defects in the sold item that the purchaser hates and because of which his desire to buy is reduced, the seller must state it even if the purchaser does not ask him about it.

Al-Kharshi said in Sharh Mukhtasar Khalil:

“Every seller whether it is in Murabaha or other must show what the purchaser hates about the purchased commodity, and his desire to buy is reduced as a result.”

The questioner's statement that the back of the phone has slightly lost the ability to resist water, which seems to be something that the buyer hates, and therefore, it is a defect which must be explained to him.

Whoever sells such a phone without explaining its defect, the sale is valid according to the view of the majority of scholars while the seller bears the sin of concealing the defect. To repent from this, the seller must inform the buyer of the defect. If he forgives him and is satisfied with the previous cost, then it is acceptable, otherwise, he has the choice between returning the purchased item and taking the payment for the defect. If the seller is unable to reach the buyer, he should give in charity the payment of the defect while intending the reward for him. The seller is not deprived of the price of the phone in this case except to the extent that the price is increased due to deception.

Shaykh al-Islam Ibn Taymiyyah said in Majmoo’ al-Fatawa:

“Whoever sells a fraudulent item is not deprived of the price except to the extent of the price of fraud, so he must give it to its owner, or give it in charity on his behalf if it is not possible to return it. For example, if he sells a defective item (deceiving the buyer) for 10 Dirhams, and its value if it if undamaged is 10 Dirhams, and the defective item is worth 8 Dirhams. So, if the seller knows the buyer, he must pay him the two Dirhams if he chooses, otherwise, the sold item will be returned to him, and if he does not know him, he should donate two Dirhams in charity on his behalf.” [End of quote]

Whoever desires the blessing of the sale, let him be truthful in it and show the buyer the truth about the commodity and its defects if any, and he does not conceal it or deceive him in it for the Prophet’s saying about the buyer and seller: “If they tell the truth and make everything clear to each other (i.e., the seller and the buyer speak the truth, the seller with regard to what is purchased, and the buyer with regard to the money) they will be blessed in their transaction, but if they conceal anything and lie, the blessing on their transaction will be eliminated.” [Al-Bukhari and Muslim]

Allah knows best.