According to Thomas Kliche, former publisher of the Journal for Political Psychology and the chairman of the politics working group of the German Psychological Association, one of the leading causes of political corruption and graft is a perceived disparity between duties and pay. As Kliche puts it, the "burden of the politician's lifestyle" is very often not met with sufficient financial rewards.
Another factor is that contemporary public perception, fueled by the media, tends to view the whole business of politics as shady or inherently dirty. As a result, maintaining a virtuous image is often nonexistent as a factor motivating politicians to be honest.
A low level of political engagement among apathetic voters also contributes to corruption. Because voters are often unwilling to involve themselves to any great extent in the political system, it becomes far easier for politicians to pursue their own ends over those of the public.
Many politicians seek to belong to the higher classes of society as well, which can be another strong motivating factor toward opportunistically and dishonestly supplementing their own incomes. However, increasing politicians' wages is unlikely to solve this problem. Rather, the introduction of more money to the political system can only be expected to increase competition for political jobs and decrease public appetite for political engagement.