DKV fuel card and what can happen to you

For fleets a great thing actually, you pay with the card and is good. Stupid only, if you fill then e.g. at Aral on the highway (which in itself is not cheap), but then at the actual fuel price then again just 30 cents on it, remember! Apparently one speculates on the neediness of the users and the fact that because of lack of personnel always less companies have their tank costs in view. Who has had similar experiences here?