I took a cab from LIS to Lisbon city central (around Ave Liberty) and the driver charged 23 euro and told us it's standard fare. I'd read Rick Steve's book and remembered that cab fare should be around 10 euros. Unfortunately, I existed the cab first with the bags while my sister who's unaware of reasonable cab fare was left behind to settle the fare.
The instance left a negative impression as the driver seemed friendly and trustworthy. Just want to share that with travelers as taxi scams are not uncommon in Lisbon. We took the cab from the city back to the airport that the hotel arranged for us with no issue.