Well it depends on what Condition you are getting it. If it is on 3kk kilometers it will have problems. Also you are right it is a BMW this means that it is not going to be on service every end of the month :)
Also about your A3 chouse. A friend drives one A3 2.0 diesel I think it is 2005-6 year and he didn't touched anything on it for now 2 years. Except the oil services ofcource.
For that E90 I have allot of friends driving their from 1-3 years without touching them too in service and believe me in Bulgaria the roads are like fucking volcanoes, the diesel is dirty and low quality but still no problems. :)