The car we were allocated had engine problems which we discovered as we drove out. Took it back to exchange for a safe car and they claimed we must have damaged the engine. We had to pay a second fuel and damage deposit or we couldn't get another car. Now they haven't refunded the first fuel deposit.
Even more infuriating is they ask you to review them on their own website but this can only be done before your deposit is returned. Very dodgy.