One can understand why salt might be sold by the pint.  One can also understand that some folk might choose to stock up on the item by purchasing several quarts...

The interesting question is this:  Why did Peter Pugh in 1765 deem it necessary to buy "1 bushel of Salt"?  If he wasn't cooking for an entire army, then why buy a whole bushel's worth of salt?  It certainly wasn't for re-sale (as a pint of salt at 2 pence per pint was among the most inexpensive readily available commodities that could be purchased at Dupui's store). 

So what was the intent that motivated this purchase?  A strong clue emerges upon examining the nature of the Pugh family business.  Consider this other entry from Peter Pugh's ledger account:  "To Boards for a coffin and nails"... or similar entries from Hugh Pugh's ledger page:  "By making a coffin for your Negro wench."  The Pugh family was in the undertaking (mortuary) business.  They were using salt as a preservative, utilizing salt as part of an ancient and well-known method of embalming.  As 1765 was a year within the period of Pontiac's War, perhaps the Pughs were anticipating a heightened demand for their services.

As to the location from where Nicholas Dupui orginally sourced his salt supply, the family's ledger supplies an answer.  In the 1744 account pages of Edwart Boyles, we see this entry:  "To Cash paid at Philadelphia for Salt (£2, 10s.)."  That's 600 pence worth of salt.  If Dupui bought the salt at 1 pence per pint, and re-sold it at 2 pence per pint, then that would have been enough salt for the needs of 300 families (at a quart of salt for each).

The calculation accords with the known size of Dupui's customer base -- the ledger lists 167 customers on credit terms while citing yet another 212 individuals within its pages (folk that purchased on a non-credit basis).  Clearly, enough salt was stocked to meet the needs of an entire community.

However, with only 93 pints of salt recorded as having been sold at Dupui's store (to only seven individuals), such begs the question:  "How then did the remainder of the population attend to their dietary need for salt?"  The answer presumably lies in the inexpensiveness of salt... it didn't need to be purchased on credit terms.   It could be routinely obtained on a Day Book cash basis (and hence the limited number of entries to be seen on the credit-based ledger pages).  As always, the ledger itself only tells part of the story.