S.T. Dupont is less in demand among collectors than strong brands like Montblanc, Pelikan or Nakaya, so that the achievable resale value is limited. Binding valuations are generally very expensive and often stand in no sensible relation to the market value. Generally, writing instruments lose much of their value already on leaving the shop; only a few gain value over time. Recommendation: either use yourself or, for value determination, list on an eBay auction starting at €1, since there the largest interested circle is reached.