Why Don't Real Estate Agents Keep the Deals for Themselves?

[Da Shiek Woodard]

I read a lot of posts on here that look to understand seller financing. I am starting to grasp why a seller would do it (tax advantages, steady money flow, low risk, etc), but aside from Zillow and Craigslist, a lot of deals are said to be on the MLS.

At the risk of sounding obnoxious, why wouldn't real estate agents simply keep these deals for themselves if they are lucrative and require a low entry point in terms of capital?