There are plenty of soul sucking jobs that slowly damage your mental and physical health. They may seem (barely) gainful until you have to pay the piper (doctor).
But about those boiler rooms, there are one or two that just don't get the message to quit calling. They seem pretty shady, so are likely frauds. Each time, the caller sounds like they couldn't have been at it for more than a week or two. That's because they burn 'em and churn 'em.