Have just found proof that Ameritrade gets kickbacks. Visit http://ameritrade.com/tell_me_more/ page and then click on "SEC 11Ac1-6 Order Disclosure" and a new page will pop up and lead you to advancedclearing.com's site where the disclosure is posted. The kickbacks are as high as 0.5 cent per share. Have found some false facts, too. Visit Ameritrade's http://ameritrade.com/tell_me_more/ page and click on "our best execution statistics" link, and a new page will pop up. That's where Ameritrade claims their median speed of execution is approx. 1 second. Baloney. In my experience it varies between 1 and 277 seconds.
I think payment for order flow is the shadiest practice on wall street. However, it gets no mainstream press attention.