Generally, ecommerce falls under the jurisdiction of the Federal Trade Commission. Ecommerce might also fall under the jurisdiction of a specific agency: The Food and Drug Administration; The Alcohol, Tobacco, and Firearms Bureau; the Department of Commerce, The Department of Justice, or perhaps the Securities and Exchange Commission.
The Federal Trade Commission has jurisdiction over fraudulent and deceptive practices. How do rules of commerce in the physical world translate to ecommerce in the cyber world? Fluently. What is bad, is bad the same here as there. A false claim in an advertisement is a false claim within the jurisdiction of the FTC regardless of whether that ad appeared on TV or on your favorite portal.
The FTC engages in consumer awareness, business awareness, and enforcement. There is a wealth of guidance at the FTC website concerning what the rules are and how one goes about complying with them. The FTC also has authority to bring actions against violators seeking injunctions and financial settlements. Every now and again the FTC engages in a Surf Day where the Agency will sweep the Net examining websites and whether they are up to snuff.