The ultimate goal is to intimidate renters into purchasing as much insurance (Collision Damage Waiver, Liability, etc.) as possible, effectively doubling the cost of a daily rental.
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For that matter, the car rental firms routinely bundle damage waivers/insurance products into their volume/corporate contracts and still arrive at prices below the retail base rates.
I don't think it's the insurance itself that's being sold here at all. It's more more predatory than that: it's the kind of price discrimination that squeezes a premium for "peace of mind" from the segment of their retail trade who are nervous, inexperienced, risk-averse, or financially unable to accept the small risk of an expensive event. Like a payday loan—it's spectacularly expensive to be poor.