Car rental in Greece.

I have been using Economy Car Rentals for about 12 years, mainly in Greece about 4 times a year, but sometimes in Cyprus. The service varies a great deal depending on who the local car provider is. I have had very mixed experiences over the years.
Cars tend to be high mileage, 2-4 years old, although I have had one car which (going by the model) was about 9-10 years old. Generally, I am not bothered by the odd scratch or small dent, but I have had some cars which I had to refuse as they were a disgrace to be seen in!. Conversely, on the odd occasion I have had almost new cars. On one occasion, I had a brand new car with zero mileage. This was the only time in 12 years.
I have just returned from Greece. The car I had was ok, some scratches and a small dent. I can live with that. The model was a Ford Fiesta, as advertised. My beef on this and many other occasions relates to the so called "fair fuel policy" claimed by the company. On very rare occasions, the tank is actually full. However, more often than not, and it was certainly the case this time, the fuel gauge shows full but virtually the minute I drove off the fuel gauge indicator immediately starts to drop. However, when I fill the tank up, which I do many times, it takes about 30-40 kilometers before the fuel gauge indicator starts to drop. In other words, someone is creaming off some of the fuel when the car is returned with a full tank. I estimate they are making 5-8 Euros clear profit from every car they rent. Whether the company is making this profit or the employees is of academic interest. The fact remains that customers are being ripped off.
Personally, I don't give a flying fig over 5 Euros, but I hate being taken for a idiot. It's time that something was done about this sham.