This is the title given to tours that offer the tour for free and work on a donation basis. At the end you can give the guide what you felt the tour was worth. In our small and humble company, we are confident enough to let you decide what the value of the tour is.
From the start of 2020, we have to charge Entertainment Tax for use of the 'Open Air Museum of Amsterdam'. It is per person and we charge it by debit card at the start of the tour (€1,55), or with some tours through online payment (€1,89). More info: https://www.amsterdam.nl/en/municipal-taxes/entertainment-tax/
This means that the only source of income for us, is in tips. We don't receive any sponsoring or commissions from other companies, we only rely on the generosity of our visitors. Any amount is tip is accepted. In this way, anyone can join - regardless of their travel budget.