why not replace democratic elections with sale of offices by auction?
That would be a step backwards from the present system. Now those with the money get to decide who will run and have a tacit veto over their positions and actions--all without leaving much evidence behind. Then when things go south they can tell the general public: "Well, you elected these fools." And so we did.
As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."
At worst democratic election provides a way of limiting corrupt politician A's period of looting the treasury, even if it just provides corrupt politician B with his turn at the trough.
So you do not believe after all in transparency in government? The Fates are kind.