To put a number on it:

6% transaction fees you're talking about are probably in home sales. About 800B a year transacts in the US in home sales (existing home sales data: http://www.realtor.org/sites/default/files/reports/2013/emba...). In practice, that 6% number often is a bit lower for the brokers. Also, FWIW, on top of broker fees, you'll be paying attorneys, government taxes, etc.

In Chicago, to transact in and out of a house, you should expect to pay between 10 and 11% (so if you buy a house for 100k and sell it for 110k, you will break even if you're lucky).