i have found it depends on the brand and the dealer ship. some garages are good some are bad, small family businesses tend to be good, more welcoming, (not always), my experiences so far in the last 10 years.
BMW - excellent customer services, been to several always a pleasure
Audi - never made me feel good, always felt like i wasn't up to the brand standard (helpful, but while still looking down there nose)
Nissan - mixed bag - depends on the dealer ship, most don't know there prestige cars, but could probably sell you a really good deal on a micra
VW - varies on the garage, but most have been good felt welcome stowmarket, i now feel like part of the family after buying my wifes car there
Toyota - always had good customer care there especially chelmsford
Honda - another VW style garage, generally good, know there cars and helpful - best one was the one in stoke - think there nissan branch is on here
Mini - generally good, but do like to pester on the after visit phone calls
others i haven't tried
biggest thing i've found is how i turn up to them, its like the good old days of visiting the bank manager, dress smart and you normally get a good treatment. car dealers think they can smell money, so if you dress the part they tend to be good. i once blagged a z4m coupe for a weekend once. and i had a mate who got an M3 for the weekend.