In his memoirs about his personal life as a slave and slavery in general, Moses Grandy on page 65 claims that:
The proprietors, though they live in luxury, generally die in debt: their negroes are so hardly treated, that no profit is made by their labor. Many of them are great gamblers. At the death of a proprietor, it commonly happens that his coloured people are sold towards paying his debts.
Is his claim that the horrible treatment of the slaves caused them to be not profitable correct?