Crooks in politics: There is no real solution except a political culture where parties do not nominate such people and voters do not elect them.

In a first past the post system (at least in the UK) party loyalty usually means neither the positive or negative characteristics of the individual candidate makes much difference to the result. Traditionally it is estimated at 1,000 votes either way in a 70,000 odd voter constituency. There have however been exceptions.

British electors will sometimes forgive sexual scandals but they tend to be quite intolerant of financial and electoral wrongdoing.

In 1997 Neil Hamilton was the Conservative incumbent for the very safe Conservative seat of Tatton. He was accused of accepting cash in brown envelopes from Mohammed Fayed. Whatever the truth of that (a libel jury accepted Fayed's evidence rather than Hamilton's) it led to an Independent candidate defeating Hamilton (after both the Labour and Lib Dem candidates had withdrawn in the Independent's favour - a quite unprecedented development in modern British politics).

Another example is Fiona Jones, a Labour MP for Newark, who was unseated for corrupt electoral practices (subsequently reversed on appeal). At the next general election in 2001 there was an above average swing against her, so she lost the seat to a Conservative.

Of course if the party rejects the corrupt candidate but the electorate re-elect them this does not help the standard of public life. I cannot, off hand, think of a British example since Horatio Bottomley (Liberal MP for Hackney South 1906-1911, disowned by the Liberal Party in 1911, lost his seat when bankrupted in 1912, re-elected as an Independent in 1918, expelled from the House of Commons in 1921, found guilty on 23 counts of fraudulent conversion and sentenced to 7 years penal servitude).

What you do not want is a party list system where the electorate have no influence over who is elected from the list. A well connected crook from a major party may be insulated from popular disapproval in such a system.

Therefore you either need a single transferable vote system or a party list with choice one (as in Denmark or Switzerland) to combine proportional representation and voter ability to discriminate against dubious candidates of their preferred party.