Spa local in 1919

This cover was sent on 2 September 1919 from Spa to Spa with insufficient franking (5c instead of 10c) and was subsequently taxed with 10c. The postage-due stamp is one with the town name printed on it (more valuable!).
See another cover sent from Spa on the same day and also with insufficient postage.

Characteristics: 5c+5c single and 10c postage-due stamp Scott J13 Franking of 5c instead of 10c No cancel of arrival Remain of sticking label on back
Estimated value: $94 Value attributed chiefly to the postage-due stamp [Auctioned by Olivier Simons in April 2005]