Depends on the condition of your car. If you have a lot of paint defects I'd suggest having a professional detail it, it will raise the value of the car and it will sell faster. Most people will assume if the exterior and interior are in great shape you took care of mechanics as well...just my 2 cents.
2001 Topaz Blue 325Ci 64-120k miles SOLD
2003.5 Silver Gray M3 70k miles