Not nearly as much as you think, as i said, clientele systems that really is existing at this point, would be used for that. Right now let's say lobby group made of powerful interest groups like MIC or oil or finance is bribing politicians (politicians and political parties would naturally still exist under direct democracy, just in maybe different forms) but they still have their powerbase and they would mobilise all the people dependent on them for the elections. "Don't want to lose your job/grant/contract/whatever, vote like we want and mobilise people dependent on you to do the same, and so on and on from top to bottom". Just as it worked every time before.