In 1990 the Inter-Parliamentary Union dealt with 23 cases in 6 countries: Chile, Colombia, Guinea-Bissau, Honduras, Sudan, Turkey.
Parliament members spend a lot of time harnessing a business or trade union interest to their political work. There is no guarantee that a parliamentarian will not put the directorship or consultancy or other private interests before the public good.
Parliamentarians outside interests should be increasing, because otherwise they do not know the real world outside the parliament.