Nothing.
If there were worse categories i would have used them. The customer service was 0/100 stars, the worst i have ever experienced in my life. Upon renting the car we were suggested to pay for a full tank of gas. We told the employee that we were only driving to cambridge and would not be needing a full tank. He told us something along the lines (was difficult to understand 100%) that it would be the same price, so he suggested that, thats what we should do. He did NOT tell us that we wouldnt get money refunded for unspent gas!? We agreed to buy the tank and upon returning, a second employee told us we would not be getting money back for unused gas (completely new information). He told us that we could go down and fill up the tank, return it full and he would try and change the contract for a possible refund. Upon return suddenly he was not able to do anything at all to help us, except that we could write to customer service. We did upon returning home - and ofcourse, customer service will not take any responsibility for the words of the employees at stanstead. In the end, due to ridiculously poor service we ended up paying 58 GBP for about a a quarter of gas. Needless to say we were stunned by the service we recieved at Easirent.