Conducting thorough market research on your field and demographics of potential clientele is an important part of crafting a business plan. This involves conducting surveys, holding focus groups and researching SEO and public data. A guide to conducting market research can be found on our sister site, Business.com. It's also a good idea to consider an exit strategy as you compile your business plan. Generating some of idea of how you'll eventually exit the business forces you to look to the future.
Often, what happens is that we run into unscrupulous Internet Marketers (IMs) who have less-than altruistic intentions of extracting money from you rather than helping you to make it. However, this isn't something new. People have been falling for networking marketing, pyramid schemes, and affiliate marketing scams since before the start of the net.