This is a letter from a hotelier to the editor of the Good Hotel Guide.
"TripAdvisor is indeed becoming an ugly industry monster, however the public absolutely love it. Its website is the largest traffic generator to our website bar none, its huge for us and most of our bookings are generated from it.The worrying thing on the horizon is the Trip Connect feature, having to bid on a pence per click basis and offer low prices to be ranked higher. It’s obviously optional now, but you can see a time when you’re going to be forced to use it. A minority of TA users use the Booking.com function to book, and again customers are not aware of the commission rate of this. With Laterooms.com moving to 17% commission it won’t be long until Booking.com follows. All irrritations for sure but here to stay nonetheless. You might as well embrace it and just be clever in how you farm it for value.'
I don't think anyone has really answered DaveR's question about how can it be in some cases, cheaper to book with an agent rather than direct with the hotel when commission has to be paid to them.