If every charger sold lit users phones on fire they wouldn't be in business for long. The dangerous chargers generally have bad QA and inadequate insulation and

If every charger sold lit users phones on fire they wouldn't be in business for long. The dangerous chargers generally have bad QA and inadequate insulation and separation between the mains and output, so almost all of them will work at first but a few will do nasty things like dumping 120V on the output, either immediately or some time later after the insulation abrades or dirt bridges the gap.