Listings can be deleted from the Dashboard and Listings pages. Only off market listings can be deleted. When a listing is off market, just look for the Delete link button.
An important note on imported listings that are still active in the Listing Import Source when they are deleted. In this case, the deleted listing will be reimported and be put on the market in ShowMojo at the next automated import (within the next four hours). Put another way: if you want to remove an imported listing from ShowMojo it must be inactive in the source system.