Upon picking up the rental car you have to sign a rental agreement. This rental agreement contains among others the fees of the extra additions you have chosen. For example the fees for child seats, drop off charges, additional drivers, insurance or an upgrade. Signing this agreement means that you accept the terms and conditions as well as all the fees mentioned in the rental agreement. Once you have signed the agreement, you no longer qualify for any refund of the mentioned fees. In case you have any doubts or objections about a mentioned fee in the rental agreement, please ask the employee to note this on the rental agreement, on your copy as well as the original that stays with the rental company.