Act 3/1991 governing unfair competition, passed in Spain on 10th January 1991. Section 4  

(…) the conduct of an operator or professional that is contrary to professional diligence is understood as contrary to the requirements of good faith, this being understood as the level of competence and special care that is expected from an operator in compliance with the honest practices of the market, which distorts or might significantly distort the economic behaviour of the average consumer or the average member of the group receiving the practice should it be a commercial practice directed at a particular group of consumers.