This paper describes the use of conformal predictors to collect reliable positive or negative opinions of a topic from twitter users. Conformal predictors provides not only the label of sample, but also the reliability of this prediction. This feature of conformal algorithms can be naturally used to consider only opinions with high credibility of a specific topic in order to follow a recommendation. This approach can be easily extended to almost any kind of topic, the only one condition is to have previously labelled opinions of the topic that can be used for training or building the conformal predictor. The approach is tested with opinions of Spanish twitter users that recommend (or not) to watch a movie.