Good value but beware of Insurance scams at the counter.. These MUST be reported to the police

We were asked to buy additional insurance for the drive from Dubrovnik to Split, the fact that I have a global and annual insurance policy through ALLIANZ which I have been using for years and it covers all my rental car insurance needs. The agent said that I MUST buy an additional insurance for 50 Euros. I asked about it from others and they told me this is how rental car offices scam you for extra money and that i did NOT need that insurance. I feel a great disservice and would not want to rent from SURPRICE on my next visit to Dubrovnik..