Despite a drop in violent crime across the United States, the crime-scene cleanup industry has boomed. Profits for the nearly 600 firms in the United States totaled more than $99 million in 2015, on revenues of $357.5 million, according to IBISWorld, a market research group. But those profits are sometimes reaped from those who can ill afford costs that may run into the tens of thousands of dollars when insurers do not pay.