People often turn to services like Yelp or Amazon to see what people think about a business, product, or web site, but to cut straight to complaints that may not have made it everywhere, reader MrYdobon adds one word to his searches.
Google is part of our digital brains, and we trust that part to know when something is a scam. Google bill gates email, and you'll find links to Urban Legends and Snopes at the top. Google kevin trudeau, and you only need to look a few links down before you unearth the controversy surrounding him. But googling only keywords won't help when a scam is new or knowledge about it isn't widespread.
Instead, I search my keywords plus the word "scam". For example, search "some business name" (with quotes), and you'll primarily find pages hosted by the business. However, if you Google "some business name" scam (with quotes), you'll find—in addition to this comment—information you would want to consider before doing business with that business (info Gawker readers are well familiar with).
Note: Just because you get hits when googling keyword + scam, doesn't mean the controversy you find is valid. Google won't rate the quality of the information you're reading for you. You still have to do that yourself.
Disclaimer: I make no claim that Kevin Trudeau or the Bill Gates Email are actual scams or scam artists. Rather, this post is using these as examples in which a Google search can produce pages with controversial information about them.