Is it permissible to have cars repaired by a Muslim young man who works in car body repair in a non-Muslim country, knowing that he does not own a licensed shop and it is believed that his work is illegal, and would that be considered aiding in sin?

Muslims residing in non-Islamic countries must abide by the laws of those countries unless they contradict a religious text, because their residency is based on respecting these laws. Accordingly, it is not permissible for a Muslim young man to open a car repair shop without a license if that is a requirement, unless he works from his home without violating the law. It is not permissible to have your car repaired by this person if he is in violation of the applicable laws, because that would be assisting him in falsehood. However, it is permissible to have your car repaired by him if he is free from violating the law.