I learned my lesson about these sites the hard way. Hidden fees, reservations impossible to cancel or reschedule, services that were billed as "free" that actually weren't, etc. When I've asked individual hotels about this, they've told me the booking sites pay them so little money they have to nickel and dime customers for everything just to break even.
Now I only use the booking sites to find out which hotels are near where I want to go and possibly available, and I make the reservation by going to the hotel's website or calling them directly. It always works out better this way.
Booking.com is just awful. You feel like you're participating in a non-stop A/B/C/D/E/F UI test.
Links open in new tabs. It shows sold-out properties by default. Filter menu changes all the time. Obsessed about offering apartments/aparthotels. Filters labelled e.g. "Hotels + more", whatever that means. Each filter click triggers a main content reload. Changing the location resets the filters...I could go on.
Now I only use the booking sites to find out which hotels are near where I want to go and possibly available, and I make the reservation by going to the hotel's website or calling them directly. It always works out better this way.