I've sold my previous cars fairly quickly (all less than 30 days) on auto trader. Although I look at edmunds/kbb and the like, I usually go by similar cars in my areas (private and dealerships) and go from there. I tend to price them somewhere in the middle (not the highest and not the lowest) and seems to work out great. As someone stated, you have to really look at the cars in YOUR OWN AREA as prices do vary across the states. But probably one of the biggest reason (IMO) why I've sold them fairly quickly is because they all had MANUAL transmissions. Sure, there will be less people looking for manuals, but for those who really want one....there's really not many around. Hence, supply and demand is definitely on the side of the seller when it comes to 6MT.
'09 e90 AW 335i M-sport
BMW PPK 1 / BMW Perf. Exhaust and Gloss black grilles / 19" BMW 313 Perf. wheels / BMW Perf. aero side skirts and rear diffuser