Ofcourse this is not business, its absolutely haraam income. Had he informed u with regards the defect and adjusted the price accordingly, then it wouldve been a different case. Worse case is, he wont even admit it.
I had my bike's seat cover replaced a few days back. When i was in the market, the shop owner had come running to me and had been very enthusiastic in offering his service, calling me beta beta all the time
I came home and started to wash my bike. I have a habit of removing the seat to clear the dust beneath. Now i noticed that the side bolts werent original. I went back to that shop keeper. Not only did he pretend not to recognize me, he refused to even speak to me. I didnt want to create a big deal out of it, so i quitely came home