Hi, here is some general taxi information that all your visitors might find useful.
Taxis when you are at Lisbon airport.There are plenty of them. If there is a long que on arrivals, turn back into the terminal building, go left up the stairs to departures and basically walk out when most people arrive. Oposite there are normally dozens of taxis waiting. So now your in your taxi and have given your destination.
The general rule is as follows; tarif 1 is during working days from 7 am until 9 pm, this is the lowest rate and applies within the city limits. After 9 pm it is tarif 2. Saturdays and Sundays are always tarif 2.That should cover most visitors to Lisbon. Tarif rates 3 and 4 should NOT be used inside Lisbon, because those are rates for when you go outside the city. The airport is still concidered within the city. There will be a small fee for luggage in the boot.
Taxis used to try to rip people off but only very seldom. This was before the time that the rate which the taxi is charging is displayed on the rooftop display. Check it yourself. If you see any taxi that has e.g. number 3 on its roof, check the back of the taxi and it can say for example Cascais or any other town but Lisbon. He can charge tarif 3 because he is outside of his town. Not that rate 3 is so expensive. Rate 4 is and you better get out or stop the taxi.
Starter fees of taxis in Lisbon are €1,90 I believe. If you ask your hotel to arrange a taxi for you because you have to go to the airport early, make sure that they hire a public taxi and not a private one. Those guys will charge you €25 to go to the airport whereas a normal taxi would be let´s say €10.
Most older taxi drives do not speak english, some younger ones do. I have found them in general very polite and honest. Do wear your seatbelt, portuguese drivers are crazy! Tips, give them something small like €0,50 and they will be happy. Nothing more is required and certainly not custom.