Interested in cancelling or clearing a ships current trade orders? With the just released 1.17 patch, Egosoft has added a way. Just follow these steps...
Info -> Property Owned -> Ship -> Select DE (Detail) -> Select Captain Details -> Highlight Pending Trade
There should be a Clear All button available at this point. Just choose that and it should wipe out the Pending Trade.
It doesn't seem like this fixes stuck trades, like in the deliver 100 Energy Cells plot mission. I had to initiate a new trade for it to show.