A bad locksmith is a locksmith who engages in unethical or illegal practices, such as overcharging for services, damaging property during the job, using low-quality or inappropriate tools and techniques, failing to provide adequate security advice, or even engaging in criminal activities such as stealing or duplicating keys for nefarious purposes. It's important to do your research and choose a reputable locksmith with a good track record to avoid falling victim to these types of scams or unethical practices.