Between the 1.8 update, the soon-live name changes, and the fact the plugin is still abandoned, it's time to drop Duckshop. The plugin will be officially removed within a few days. If you are only using SignShop for trading, you should be mostly unaffected.
The difference between the shop types can be seen on our wiki entry for shops:
pearlmc.net/wiki/shops/

Any Duckshop signs found marked empty are subject to removal and shops in official areas may be closed if they are still exclusively or majorly using Duckshop signs.

For reference, this is the thread forewarning about the removal
http://pearlmc.net/threads/new-shop-plugin.19/

 

RIP Duckshop,

You were easy for players to use however you did not keep up with the times (and items), we as players will miss you . . . as administrators . . . not so much.

******* taps plays quietly in the background *******