@nonu
These BERLIN overprints will usually only sell at elevated prices with genuiness certification, since there is too many forgeries around.
Having said that you can try selling and if they are genuine very good. But you need to be careful since if they proof to be false the buyer may not be happy. And in
ebay, for example, if you say genuine and it proves false, the buyer can either ask for returning the stamp or he can demand you deliver a genuine one