I have usedTripadvisor.com on many occasions to find hotels to stay on my travels. Some hotels listed by TripAdvisor do not take direct bookings on the internet.
As a result when you search for availability of dates, your site indicates that "The hotel has no rooms available for the dates requested".
This is NOT correct what it should say is that "This hotel does not take bookings via the web and that one should call the hotel dorect to check availability. "
This reply is available on booking.com and even the HiHostels website.
Tripadvisor needs to rectify this in order not to give yhe impression to potential customers that the hotel has no availability when it actually does.
Tripadvisor should advise customers to call the hotels direct for availability for those hotels that stillpdo not use an automated web booking system.