Construction law in the Netherlands.

An extra invoice is not automatically right or wrong. Compare each item with quotation and later agreements. Identify included work and actual changes. This concerns private commissions.

Fixed prices, estimates and payment for hours and materials allocate risks differently. Check actual agreement, rates and limits. The word quotation alone does not identify the pricing model.

Extra wishes may create additional work. Check timely warnings of increased costs and any exception or separate agreement. Absence of a signature is not decisive alone.

For an estimated price, the starting limit is ten percent without the required timely warning. Warning must allow choices. This is no general surcharge for every fixed price or order change.

Costlier materials, unexpected ground conditions and additional requested work have different causes. Ask which agreement supports each higher charge. Assess provided information and warnings too.

Write which items you dispute and which support is missing. Separate disputed and undisputed sums. For large amounts, collection threats or stoppage, consult a construction lawyer before major payment measures.

Read the full article and sources. General information does not replace advice about your own situation.