I have discovered the following during the booking via hostelclub.com:
Let’s imagine, I have selected a single room for 1 night that costs 25.11 EUR. The Hostelclub.com shows the total deposit as 100% of the price (2.51 EUR).
Once you press the “BOOK” button, the page shows that the total price to be paid is 25.11 EUR (the same) but deposit to be paid grows up to 4.51 EUR as it includes service charge of 2 EUR that drops out of sky.
Therefore, the total price to be shown to the customer should be 27.11 EUR.
This small trick generates hundred thousand of eur for the smart owners.