SZYMKOWIAK , Andrzej. Group Buying Portals as a Tool for Promoting City Break Holidays. Studia Oeconomica Posnaniensia, Poznan, Polska, v. 2, n. 3, p. 136–153, 2014. DOI: 10.18559/q8rxaq26. Disponível em: https://journals.ue.poznan.pl/soep/article/view/3223. Acesso em: 3 sep. 2026.