Airport taxi service

I had heard that the taxis at the Lisbon airport often overcharged customers (particularly tourists). Apparently, it is common practice not to use the meter when airport transfers are involved. For instance, several people I talked to had paid anywhere from 8-17 Euros for a transfer from the airport to a city hotel. I was told by a friend to plan for no more than 10 Euros per journey, with a possible 1-3 Euro add-on for night trips.
With this in mind, the airport does sell a prepaid journey ticket for 16 Euros. However, this was still much more than most of the people I talked to paid, so it is doubtful that it will save you any money(see website for info http://www.toandfromtheairport.com/lisbon.html). Your best bet is to talk to the driver before beginning your trip to determine what the price will be and then to decide whether you want to try another cab.
Also, I have heard from other people to try walking over to the departures gates rather than arrivals to try to save some money.