The signs I look for in spotting a successful business is if they have massive amounts of traffic being constantly funneled to their business.  I believe this is what divides the smart, and genius marketers from the beginner, baby marketers.  Most internet marketers stay at the baby level of traffic and fail to break out above this level.  Unfortunately, driving traffic to your web site is something that requires a lot of effort and creativity in order to accomplish.  Most web sites gain their targeted traffic by building link popularity, and this can be hard to do if you are not creative.  Being innovative and creative is the key to gathering huge swarms of visitors to your website.