When you over-declare the item value (when the insured value is higher than the real value of the item) the insurance company will not compensate you for the full value.
In case of under-declaring the item value (when the real value of the goods is higher than the insured value), the insurance company will payout a % of the insured value, as in the example below:
The insured value is higher than the real value of the goods.
Goods real value: 150 €
Compensation value: 150 €
The insured value is lower than the real value of the goods.
Insured value:100 €
Goods real value: 162.27 €
% applicable to the insured value: 61,47 % (Insure value /Goods real value)
Compensation value: 61,47 € (Insured value * % applicable)