Most start blathering about grey imports, differing specs or not being shown as the first keeper of the vehicle on the V5. The last bit is true from some of the cheaper suppliers, but if you are saving say a grand off RRP will it cost you that in it's value when it comes to trade in time? At the end of the day the number of owners shouldn't effect the value of a vehicle, but it is used against you to beat the price down with regardless.
Some suppliers though actually are main dealers, on the Civic Type-R there are some good deals to be had from what is actually a Honda Dealer in Solihull.