Redfin, is actually a real estate sales agency... just like any other agency... (Like Coldwell Banker, Re/Max, Century 21)... and their website, pulls their information from the MLS.
Talk to several agents, and ask them what they offer beyond the basics. Different agents can offer different marketing plans, even within the same agency.
There is a lot of agent to agent info that gets passed along behind the scenes too. We do lots of word of mouth marketing. If we bump into an old friend that lives in a neighbohood where we have a listing, we tell them to tell their friends about our listing. We also have a lot of agent to agent conversation. Each agent has buyers looking for different areas and features.
Lastly, we do open houses with craigslist marketing, posts on our Facebook Page, a blog, Twitter, and any social network marketing we can.