Red Jeans and Elbow Grease

Years ago, many an unsuspecting youngster was sent down to the shops to procure a tin of Elbow Grease, only to find a knowing, smirky grin, and the shopkeeper's chuckling assurance that no such item was in existence.
Off home the child would then march, empty-handed, hands bunched into ready fists, boiling with rage at the adult who'd played such a trick, smarting equally from the shopkeeper's gloat.
Poor Mater: it happened to her the other day. Except that Elbow Grease wasn't the object; and besides that, the thing does, in fact, have a place in the world.
Red jeans.
It was all that Mater wanted. She'd seen a nice little advertisement showing some merry people clad in red jeans and, although she'd never seen such things before, she decided- why not red jeans? Why not.
Off she went, gliding into a store in town.
"What?" the youth gasped at her. "What did you say you were looking for?"
"Red jeans," echoed Mater.
"Never heard of them," announced the fellow. "They don't exist."
"But I saw-"
"No such things."
"There was an advertisement-"
"No."
"Maybe another store would have-"
"They don't exist."
He was emphatic about the item's lack of existence. The discussion didn't so much draw to a close as it was slammed shut with a cling and a clang and some suitable, rusty-key-turning sounds, punctuated by the assistant tossing the proverbial key down his gullet and swallowing it.
From the proverbial key dangled a key chain which bore a miniature portrait of some happy people bedecked in their red jeans, but he gulped it too hastily for a terrifically baffled Mater to point out and use as evidence in her quest.
To prevent the fellow from performing such flimsy half-jobs in the future, I'd make sure to send him on a long, long journey to the shops to get a tin of Elbow Grease.