Cities, states, or countries need to band together and agree/legislate that reservations can only be made on official sites that charge no commission. Keep the money local. Simple.
As the tech become easier to connect everyone, this will become the norm.

By stealth Booking.com have effectively taken over the selling activities of too many hotels. Now they are flexing their muscles and bully the weakened hotels into worse conditions. Hotels: Take sales back in-house!

Caribbean hotels speak with '' forked tongues ''. Within the last 6/8 months I have made three bookings with Bookings.com for myself. On all three occasions the hotels have called me to cancel and book direct at a better price. Enough said.