John Camden Hotten, The Slang Dictionary; Or, The Vulgar Words, Street Phrases, and "Fast Expressions of High and Low Society (1864) has a couple of interesting entries for job:
JOB, a short piece of work, a prospect of employment. [Samuel] Johnson describes JOB as a low word, without etymology. It is, and was, however, a Cant word, and a JOB, two centuries ago, was an arranged robbery. Even at the present day it is mainly confined to the streets, in the sense of employment for a short time. ...
JOB, “a JOB lot," otherwise called a "sporting lot," any miscellaneous goods purchased at a cheap rate, or to be sold a bargain. Frequently used to conceal the fact of their being stolen, or otherwise dishonestly obtained.
As Hotten reports, Johnson's Dictionary of the English Language (1756) does not provide an etytmology for job, and it offers these as the first two definitions of job as a noun:
JOB. s. 1. A low mean lucrative busy affair. 2. Petty, piddling work ; a piece of chance work.
Early occurrences of 'job lot'
One of the earliest occurrences of the term "job lot" turned up by a Google Books search is from a transcript of the case of *Cornish & Sievier v. Keene & Another* (January 30, 1837), a patent case heard in the Court of Common Pleas:
Robert Cox sworn. Examined by Mr. Attorney-General.—I purchased some goods of Mr. Godby on 31st of May 1833; it was called a job lot ; I am not aware I ever bought any other. I made the purchase in behalf of Mr. Lee ; I am acquainted with the nature of the alternate web [for weaving]. I cannot say any of those were of that quality ; what I recall of them was, that they were of original quality.
Also, from "Commercial Solicitors," in The North of England Magazine (May 1843):
The two most celebrated commercial solicitors in Manchester are Mr. Pixton, of the house of Rapperton and Rodney ; and Mr. Leadbeater, of the house of Murdockson, Nephew, and Fox. Both of these gentlemen are in the same line of business, therefore of course they are rivals. ...
Mr. Leadbeater, on the contrary, is blunt and gruff in his demeanour, offering his goods to your notice as if he did not care the value of a bill-stamp whether you buy from him or not. ... He talks as long as he can compel you to listen to him, pouring his words into your ear against the stomach of your sense, and interlarding his discourse with offensive expletives ... suggests the probability of one of his principles, Mr. Murdockson, (who, by the way, has published a pamphlet on the corn laws) being requested to stand for the borough in the event of a dissolution—and concludes by offering you a "job lot" of Bandannas at fifteen per cent under prime cost.
And from "Narrative of Law and Crime," in The Household Narrative of Current Events (September 27, 1851):
On the 18th, Charles Whicher, green-grocer, was tried for Staeling, and John Saward, a draper in the Commercial Road East, for Feloniously Receiving a case of merinos and mousseline-de-laine, the property of the South-western Railway, to whom it had been intrusted for conveyance from Southampton to London, for Messrs. Candy. ... The three [Whicher and two other men] sold the property and divided the proceeds. Mr. Saward was the purchaser. He met the others at a public house, and agreed to give 56*l*. for the good ; he paid the money by instalments ; he got a receipt signed "H. Roney" ; the goods were called a "job lot." The wholesale value of the property thus purchased was 147*l*. Saward sold some of the merino in his shop at 4*s*. l1*d*. per yard ; the wholesale value was 10*s*. 6*d*. Serjeant Wilkins contended for Saward, that he had fairly bought the goods as a "job lot," and that he had behaved like an innocent man when the officers came to his house about the goods.
It thus appears that a "job lot," in the first half of the nineteenth century, referred to a one-off batch of resellable items, often either of substandard quality or of odd quantity, and not always obtained from a well-established and legitimate source of supply. Then and later, according to Hotten, the term job retained a somewhat unsavory character, owing to its origins in the 1600s as a cant word.
But John Sangster, The Rights and Duties of Property (1851), and Henry Mayhew, London Labour and the London Poor (1851), describe the "job lot" market as constituting a full-time trade for a whole class of middlemen and purveyors, and as involving legitimate commerce.