It's the way of the world now. I hope you can figure out a way to advertise a personalized service that people will pay for. Something like on-the-ground knowledge, or a package of things to do that goes well each hotel, something that maybe Booking.com doesn't cover.

In real estate market in the UK, Purple Bricks is a kind of Booking.com type solution, and they are really awful, as they offer no actual service whatsoever in selling your house, so you have to show people round yourself, and you really have noone advocating with the entire market for the best price. But folks use Purple Bricks because they charge a low fee. The fact that you get a low level of service, which might mean you don't get the best price, doesn't register with people.

It's an uphill battle trying to compete in this market, but I guess what you must do is figure out what value a human being can add, and advertise that. Good luck.