A seller making the purchaser aware of the defects of the sold commodity

Q: I have read the following Qur'anic Verse: O you who believe! Eat not up your property among yourselves unjustly except it be a trade amongst you, by mutual consent. And do not kill yourselves (nor kill one another). Surely, Allâh is Most Merciful to you. (Surah Al-Nisa', 4:29). I was an official in a car agency and this agency purchases spare parts from Al-Tashlih (stores that sell used spare parts) and installs them in clients' cars instead of installing new spare parts even though there are new spare parts available. The payment they receive from the clients is in return for replacing the damaged parts of the cars with new spare parts. It should be noted that these damaged parts are sometimes basic parts in the car such as the front differential which, if not working properly, may lead to accidents and deaths and also the car wears out quickly. This process forces the client to return and replace the spare parts and pay for fixing them another time. Then again the agency brings him old spare parts from Al-Tashlih. They do all this to make more money. (Part No. 13; Page No. 217) Also, the manufacturer of the spare parts gives every purchaser a guarantee to use the spare parts for a certain period of time or a specific distance and this is common in car agencies. During the period of guarantee, the manufacturer undertakes the responsibility of fixing any damage in the new cars. However, in this agency, they agree with the client to replace the damaged parts within the period of the guarantee as follows:The damage in the car may be minor that could be fixed simply, but the officials in the service department agree with the client to replace the damaged part with a new part in return for half the price of a new spare part. After that they install the new spare part in the car. He pays for the new spare part and the installation fees even though they are covered by the guarantee given to the client by the manufacturer. Moreover, they sell the used spare parts to other people without informing the manufacturer or the client which causes the manufacturer to incur losses.The question now is: Was my work in this service agency unlawful? What is the ruling if I return to work there again? Does the Qur'anic Verse mentioned above apply to work in this service agency? Does my silence make me an accomplice with them in these acts? Do I have to inform the authorities? It should be mentioned here that these acts are still being practiced. When I advised them to stop, they became hostile towards me. I appreciate your advice. May Allah reward you with the best.