17.5 seems pretty low...specifically ask why it is that. Ask to see the "Black Book" price. They used Black Book to price my X5 2003 with 40,000mi. They said Blue Book was off, and Black Book was the best.
For the 328xi, try to get the 41,239 to "a nice even number" like 41,000 or 40,500. They can do it if you have the patience.

__________________
T