Thanks to both of you for your detailed replies!
I must admit that I was very surprised that this sort of thing would happen in Sweden
I will certainly be better prepared next time! One problem was that I wasn't going to the city centre, so the Arlanda Express (which I have used previously
) wasn't appropriate.
I picked the taxi up at Arlanda (I don't remember which line it was), to Kista. I was charged SEK445, the "correct" fare according to the hotel (and confirmed by my return journey) is SEK300-320.
The taxi company was called "Taxi ABC", I think my flight arrived around 14:00, and the first receipt the driver gave me was for a journey between the times 09:17-10:55, and a distance of 87.22km. Registration number of the taxi was YZG025, and the driver's name was Mahmud Rojhan (or Roshan). Hey, I even have his mobile phone number
I guess I'll just chalk this up to experience! Thanks again.