Seeking a valuation of my flat in Brussels

I am planning to sell my flat in Brussels to finance buying a flat in my own country in preparation for my retirement. While I know I could go to a locl Estate Agent for a valuation, I was looking for someone who could not only value the property realistically (i.e. not over value it to get my buisness) but also advise on what I need to do to improve the value of the flat. But a realistic valuation is my main objective. Any ideas/advice gratefully received. Thank you, James