Ads having taglines such as Fastest growing, Country's best and largest selling are based upon the principle ofa.Likingb.Authorityc.Commitmentd.Social proof

The taglines such as "Fastest growing", "Country's best" and "largest selling" are based on the principle of Social proof.

Social proof is a psychological and social phenomenon where people assume the actions of others in an attempt to reflect correct behavior in a given situation. In the context of advertising, social proof often comes in the form of testimonials or reviews. When advertisers claim their product is the "fastest growing" or "largest selling", they are using the principle of social proof to convince potential customers that since many others are buying and using their product, they should too.