APA (7th ed.) Zitazioa

ebrary, Inc, Gutzman, A. D., Muller, A., Pfledderer, D., & Gibbons, T. (2002). Buyers' guide to search engine optimization firms: Who should you hire? how much should you pay? (2nd ed.). MarketingSherpa.

Chicago Style (17th ed.) Zitazioa

ebrary, Inc, Alexis D. Gutzman, Anthony Muller, Donna Pfledderer, eta Tim Gibbons. Buyers' Guide to Search Engine Optimization Firms: Who Should You Hire? How Much Should You Pay? 2nd ed. Portsmouth, R.I.: MarketingSherpa, 2002.

MLA (9th ed.) Zitazioa

ebrary, Inc, et al. Buyers' Guide to Search Engine Optimization Firms: Who Should You Hire? How Much Should You Pay? 2nd ed. MarketingSherpa, 2002.