I hired a car via the Easycar agency in the U.K. on the understanding I would get an upgrade to a Citroen C5 or equivalent.
When I collected the car from Avis in St Malo, France, they gave me a Seat Altea. As we were in a hurry we hadn't time to argue with Avis - it really wasn't their fault as Easycar had offered the C5 off their own accord. The Seat was a much inferior car. It was too small, noisy and lacked the comfort of an executive standard C5. It also had some built in so-called economy system, which meant it cut out when one pulled up at a junction or roundabout. This was highly dangerous as no explanation had been given of this unusual system. It took considerable time to discover how to restart the engine. All told, it spoilt what was intended to be a comfortable and enjoyable tour of the continent.
On return to the U.K., I complained to Easycar - they didn't want to know and kept referring to their statement that it would be a C5 or equivalent. They refused to acknowledge the Seat was not an equivalent vehicle and refused any compensation.