Taking a taxi is luckily not a problem in Nuremberg. Every cab must be yellow and is registered by the city. It’s generally cheaper to call/let call for a taxi. However, if you need to take a taxi from the street, you can feel quite save and the price difference is not really big. There are many companies providing this service. Just ‘’google’’ them or ask in your hotel for theirs trusted partner. In some taxis it’s even possible to pay with a credit card, but I would still recommend to have a cash on you.
May you feel like that the taxi driver is trying to charge you too much, he must always be able to give you a bill for the ride.