The origin of the term "selling oil" comes from the fact that oil sellers in the Edo period used to chat while pouring oil to keep occupied (oil at the time was highly viscous and took a long time to pour). "selling oil" is a Japanese idiom meaning "to dawdle on the job"

Really... Where are they selling oil!?

And I relied on you to do the shopping...

Her ghost-half is selling (lube) oil.