We got 2 major food intoxications in restaurants in Algarve. We did present a complaint (in the book of complaints, analysed by the tourism bureau and the city hall) at one of them but never received an answer.
The complaint we presented was about having asked for grilled fish (for me, on diet) and instead beeing served a huge fish head ('a la meuniere', that is, fried in butter). We had to pay around 35 euros for the head fish alone inspite having eaten nothing since it was disgusting. My husband did eat the appetizers (homemade liver pate) and got terribly sick the following day and for the rest of our holidays.
The next day at breakfast I was still disgusted with the look of the enormous fish head (with eyes, and teeth) in my plate.
One year later I went to the city hall to ask about the complaint and it was still on someone's desk. I later asked about that complaint at the tourism office (Regiao de Turismo do Algarve) and never received an answer.
In case you were wondering this happened at the Restaurant Vila Velha, in Sagres where we also got food poisening (in another restaurant, obviously) with shelfish.
We've stoped going to the Algarve for our holidays and have been chosing another european beach destinations (Spain and France) where we pay a lot less and get uncomparable better service.
If you're traveling to Sagres, a word of advice: stick to the restaurants in the pousadas (Fortaleza do Beliche, Pousada do Infante).
There is also a great pousada restaurant in Sao Bras de Alportel.