Have used booking.com a couple of times. However, the last few times I have gone on line directly to hotel websites, and to get better rates. As an example... Booked a hotel in Trim, Ireland two days ago for €85 while at the same time, the booking.com rate was €106.
I get various advices from booking.com such as 'lowest rate' 50% discount etc?, special rate €25 etc. Etc. But when searching the available hotels, none of those statements are true, even on the 'offers' via booking.com.
In Ireland at least, you will get a hotel room cheaper directly from the hotel either on line or by phoning.