Then again:
“I have heard that schlock, meaning junk, comes from schlag – to hit, as if the merchandise had been hit and bruised. However, the correct etymology stems from a Lower East Side peddler whose last name was Schlackman.
Schlackman specialized in buying damaged merchandise from other peddlers and selling it to greenhorns at full price. His competitor was a Syrian Jew by the name of Raphael “Fat Ralphie” Dweck, a true reprobate who accepted merchandise that even Schlackman would never touch, and who met his end at the hands of the Mafia during Prohibition (during that dry period, Dweck distilled arak from banana peels, dung, and wood; he sold it to a speakeasy whose owner died of its effects, so that the owner’s brother iced the esteemed distiller).
Other pushcart merchants, when stuck with bad merchandise, would scream out “Schlackman” or “Dweck” depending on just how bad it was, so that one or the other entrepreneur would come running, ill-gotten pennies in hand, to purchase the detritus at far below cost, only to sell it later to some unsuspecting mark at a price far above its true value.
Eventually, the -man was deleted from Schlackman, (the A was always pronounced as AH), and Dweck, a name often uttered in an incorrect fashion by Ashkenazi peddlers and Irish cops alike, became Dreck.”
(quoting a shtick post I made years ago on Usenet)