I used Carwow last year, very straight forward, contacted the dealer that had lowest price, paid deposit, picked up car two days later, couldn't be better. Some people get prices from Carwow, DTD, etc then go to other dealers to get them to compete, which seems good, but if the practice carries on the dealers that offer good discounts via Carwow etc will lose business and customers will end up paying higher prices. Mate of mine also recently got a new Golf R with £7K discount.
*One thing to be mindful of, check if they have the cars in stock.
