This is the awful experience I had while using the booking group services (https://www.bookinggroup.com): I rented a car to inter rent through booking group web site, which should be picked up at barajas airport in madrid. I also booked a full insurance offered by booking group on line, which they charged to my credit card immediately while the rental was processed. When going to the airport to pick up the car, inter rent did not accept the insurance sold to me by booking group and offered to me the opportunity of getting another insurance which was much more expensive, up to the point that the rental tariff was not competitive at all, so I canceled the reservation. Booking group tells me that they are not refunding the insurance I paid to them despite it was not accepted by their partners and the rental never took place. Be aware of booking group fraudulent practices.