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Most companies will include the legally required minimum liability insurance.
Some (like Hertz at the Cancun airport) will hold you hostage for hours to pay for additional insurance if you want your reserved car.
My last rental there was over 3 hours waiting them out while they tried to extort me for “only an additional $30/day! (for insurance or ‘upgrade’)” before they gave up and gave me the car at the price I booked.
Everyone who got a car faster paid the extortion.
It probably would have taken longer, but I was making a pretty big scene at that point.