I have been using booking.com for over 8 years now and I've observed that what you see is what you get. I most often got better deals through booking.com than when I go directly to the hotel/apartment website. I also find the trail of customers' review on booking.com very helpful as it at least provide some guidance on which properties or locations to avoid when searching for decent hotels/apartment. The search and filter engines are also great for quickly narrowing down your search.