And if its a new car make sure its had the latest software update as mine got recalled due a software bug which affected certain airbags in the car. it probably will of had this done but no harm in asking them.
An obvious one, but check every inch of the paintwork. Mine had a very small scratch on the front wheel arch, about as big as a little finger nail (which was later fixed foc). Had I driven it away, I guess it would have been my problem.
The Panda has the same feature, but it doesn't work quite as well because the weight of the key on the 500 helps to stop it falling off. (The Panda hasn't got a locking fuel cap).