The Board of Appeal deals only with a complaint if you have approached the rental agency first, and the approach did not result in a satisfactory solution for you. It is highly recommendable for all private consumers to approach the counterparty in writing.
Should the approach not lead to any satisfactory outcome, you may raise a complaint, if the following conditions are met:
A fee is to be paid in order to cover the treatment of the complaint. The fee will be refunded if your claim is completely or partially sustained. The fee is 40 Euro.
The Complaints Board may hear any case concerning matters related to the contractual obligations between the parties. I.e. lack of cleaning, absence of hot water, low temperature in a pool, lack of contractual service from the contract party, and when one of the parties fails to fulfil a contractual term. Cases concerning personal injury or damage to property can not be processed.
You can read the regulations here.