I don't see any rule forbidding it, but it is a bit of a taboo subject. I think for most people, including myself, it's just personal. Price may be subject to your local market, subject to the dealer and salesperson you dealt with as well as how well you negotiated. In short, there are too many variables for us all to suggest that you got a fair price.
Most discuss relative to invoice price, so maybe this will help you... and I'm not sure if posting the below is even allowed, or frowned upon.
|My BMW 2013 335i Sedan (Jul 12)|
|U.S.A. Port of Entry|
|B45||Estoril Blue Metaliic|
|4AB||Dark Burl Walnut wood trim|
|KCDF||Venetian Beige Leatherette|
|2PE||18" M light alloy wheels Star-spoke style 400 M with mixed tires|
|205||STEPTRONIC automatic transmission|
|ZMM||M Sport Line|
|688||Harman Kardon surround sound system|
|Del||Destination & Handling|
|Gas||Gas Guzzler Tax|
|TRA||Training Service Fee (Excludes Euro Delivery)|
|Total (Without Taxes)|
|See and Modify this config on www.BmwConfig.com|