There are 2 taxi lines in operation at the International Arrivals. One is for reputable companies which pay a fee to the airport. These companies have a maximum fee they can charge to Stockholm and will not rip you off. They include : Taxi Stockholm, Taxi Kurir and Taxi 020. There is also a line where all other taxis have to try to pick up passengers (usually quite aggressively). These cabs may try to rip you off by overcharging or skimming your credit card. Only go with one of the reputable taxi companies.
There are also companies trying to impersonate Taxi Stockholm by having an identical name to them. The real one´s logo looks like this: http://www.taxistockholm.se
Be safe and happy travels!
