Prohibition against detournement de pouvoir - An administrative authority may not use a power to take a decision for a purpose other than that for which it was conferred.  Principle of legitimate expectations - The aroused expectations in which an interested party may have reason ably trusted, must be honoured  Principle of legal certainty - When the administration is guided by a set policy, it may not unexpectedly shift direction when citizens suffer demonstrable damage from it.  Principle of proportionality - He adverse consequences of an order for one or more interested parties may not be disproportionate to the purposes served by the order.  Principle of equality - Equal cases must be treated equally and unequal cases must be handled to the degree that they differ.  Obligation to balance interests - In making a decision, the administration always has to weight interests, in so far as no limitation is placed on this duty by a statutory regulation or by the nature of the power to be exercised.