I rented a car using rentalcars.com from HERTZ in Malaga, Spain. I ended up paying over four times more the price that I have already pre-paid on-line for this reservation. I had pre-paid 120CAD which was clearly stated as the total for the rental but had to pay Hertz-Malaga additional 300 euro (about $480CAD) just to have the vehicle insured without deductibles + their local fees.
I'm sorry that this was a surprise for you, but it's not really a scam. If you chose to purchase the 0 deductible CDW, then you have to pay their fee for that. Regarding the prepaid amount that was stated as total for the rental, I would venture to say that the wording included the fact that CDW insurance was NOT included and possibly also stated that local fees were NOT included (or at least it did not say that they WERE included). I say that because those add'l costs/fees are rarely included in the initial base rental fee.
If you feel that you were legitimately 'ripped off', then you need to challenge those fees with Hertz directly.
Not sure if it's a scam or a misunderstanding. If Hertz told you that you could have the car only if you purchase the insurance, it might be a scam or it might be the law. Whether you already had adequate insurance through a credit card or enough credit for a deposit, which can run into the thousands, can be factors. As Nancy said,local fees are always to be expected, totally normal.
Can you be more specific about the reason for the insurance. Perhaps rentalcars.com was happy to take your money, quoting a low price but didn't make conditions clear.