Hiya

Trying to book car hire for my parents for three week stay in October this year and have found a deal with Dollar. However I have been told that the car hire charge is based on the car being empty and a tank of fuel will be charged when they collect the car. I was told that they do not over inflate the prices and a full tank should be no more than £25.00 they charge pump prices.
Is this correct or has anyone been badly overcharged with this clause?