It's not just the high end brands Tracy, most Audi dealers wont have a retail car for sale on their forecourt unless it has Audi history.True Tony but certain brands won't buy back or if they do they insist it goes through there own workshop for main dealer last stamp in the book even if said car was serviced recently and doesn't need servicing.
If they do agree to take it back they will really punish you on trade in price for non main dealer stamps.
I am talking top end marques not going to name any of them but do know a few.
Not sure about BMW, but I wouldn't be surprised if they're the same.
But for warranty issues you just have to use approved parts, and use a Vat registered garage, like Tony says.
I use independents once my cars are over 5 years old, or occasionally I'll use the main dealers if a car has a full dealer history, just to carry it on.
But the prices are getting ridiculous.