Taxis in Germany are well-regulated so you very rarely have to worry about getting ripped off. All tariffs are the same regardless of the taxi company being used and there is a day tariff and a more expensive night tariff. Officially, if you are carrying luggage you will have to pay an additional surcharge of €2, but not all taxi drivers include this. Some taxis accept credit cards and you can see this by the stickers, usually in the back window. If unsure, ask beforehand. Those who don't accept cards can drive you to an ATM. Most drivers speak a smattering of English due to the 50,000 Americans living in the region.