My experience is different. I provided evidence to booking.com that another website offered the same room on the same day for 10 euros less. My room was prepaid, that means I already paid booking com in advance, which then pays the hotel. Booking.com confirmed that I qualify for the price match guarantee if I can produce an invoice from the hotel - knowing that many hotels dont issue an invoice if they are already paid by booking.com.

My view is that here the burden of proof of payment is with booking.com as I already paid them. Its just 10 euros, not the end of the world for me, but it destroys the brand reputation for me when a promise is made and then the company tries to wiggle its way out of responsibilities they themselves established.