It may not even be money. There are a lot of ideologues out there who will do the job for free.
I think it is important to remember that elected representatives are analogous to legal counsel—- they are duty bound to do everything they can to advocate for the wishes of their clients or constituents. The constituents who elect public servants do not make their decisions lightly (perhaps the economy of a certain district would benefit from more liberalized industrial emission regulations). It doesn’t matter if the public servants believe what they say, they know they have to advocate these policies to best serve their constituents.
The question is who they view as their constituents. Often it's not the voters but only a very small subset. In modern Washington politics they will also put the priorities of their party above the voters.
Public servants (in the USA, regardless of party) who do not have the support of a majority their (voting) constituents seldom keep their jobs past the next election.
You still can misinform the majority of the constituents to stay in line with the interests of the small number of the people you really listen to. I would argue this is happening with health care, tax cuts and a lot of subsidies.
That's pretty much all politics, for the history of mankind.