Shoe clerk

I was just reading the column by John Vorhaus in the June 30, 2010, issue of Card Player magazine (vol. 23, #13), p. 74. I was intrigued by his use of a term I don't recall having run across previously:

[Y]ou open an unraised pot for $20, which is not a bad raise with pocket aces,
since you want to thin the field, ideally to just one player, and a bet of four
times the big blind will drive out most of the shoe clerks.

It's not hard to tell the intended meaning from context, but I wanted to see if this is something idiosyncratic to Vorhaus, or more widely recognized. I quickly found this definition, here:

shoe clerk
(n phrase) 1. A player who does not stay for a raise
(with the implication that he is dropping out of fear) or, particularly in a
no-limit game, for any large bet. 2. Someone who is not serious about playing a particular pot, and thus will not call a raise. For example, for
definitions 1 and 2, you might hear an aggressive player say, “Let’s raise and
get the shoe clerks out.” Also known as ribbon clerk. 3. A weak player.

So there ya go.

Where did it come from ? I don't know. The obvious guess is that a shoe clerk is somebody who is always bending over, reaching to the floor, so by analogy a player who has dregs for a hand. But perhaps it came from the insinuation of weakness, a shoe clerk not being considered the manliest of occupations.