People have been buying cars in a similar way for years.
When it is time to change his car (every 2 years) my son in law visits the local dealers and has test drives of the various models he is interested in. Once he has decided on a particular model he then goes on the internet and browses through all the brokers to get the best deal.
He then places an order with the broker and the car is delivered to his door - sometimes by a local dealership. He only uses brokers who act as agents - he does not pay them - but the supplying dealership.
He reckons he has saved up to £7,000 off the list price and gets a brand new car with full warranty and only delivery mileage. He concedes however, that some of the vehicles he has bought in this way have been pre-registered so he was the second name on the log book.
He also claims to benefit by not trading in his old car and selling it privately.
I must admit that it is a method I have never tried - I have always taken the easy route and traded in my old car and haggled the best deal I could get from the dealer.