I've had a look at the advert and I think you are going to be in for a difficult time.
Firstly, wash it. Seriously? Why does anyone advertise a car for sale with filthy wheels especially one thats been for sale for months. 5 minutes just making the wheels look nice is time well spent.
But sadly the car is a bit of a no-mans-land car. I assumed it was just the business nav (We all have views as to the utility of integrated nav but on a 5 Series the dash is designed around having a widescreen and not having one looks odd) being an issue but it's more than that.
The car is entirely devoid of any optional equipment bar the 19 inch wheels. Yet it is a 530d. There are people out there who just want a 5 Series and care little for specification but for these people there are many, many ex-fleet 520d with no spec cluttering the market and these people will just buy one of those. Which leaves the 530d market to those who have decided they want a little more than just 'some 5 Series'. But these people are typically option sensitive and by the time you've decided to move up in engine you've probably lost the desire for a car with zero spec. These people are going to want at least a few extras, be it the proper widescreen, or the HK stereo, or M Sport Plus, or whatever. Your car unfortunately has none of these.
So it sits in a no-mans land - too much for the 520d crowd and not enough for the 530d crowd. Leaving the only real market the occasional bargain hunter.
This is why it was cheap when you bought it and it is also why you're now stuck with it, sadly.