Every state has business opportunity laws that require certain disclosures for you when you buy into an opportunity. Most states also have franchise laws that make even more disclosure requirements.
Online is different and yes there are many scam-buster type websites; just open Google and type scam and you'll get an abundance of sites.
All the Best
Tim Berry is the chairman of Eugene, Ore.-Palo Alto Software, which produces business-planning software. He founded Bplans.com and wrote The Plan-As-You-Go Business Plan, published by Entrepreneur Press. Berry is also a co-founder of HavePresence.com, a leader in a local angel-investment group and a judge of international business-plan competitions.