Worse yet, they had work stoppages, ran away, broke equipment, sabotaged crops, feigned illness and injury; many were more trouble than they were worth. However, I can't say I would have blamed them, but it was what it was.
Depended strongly on who put them to work and where the slaves came from.
In South-Africa from 1650 to 1825 the vast majority of slaves had been brought in from India and the Indonesian Archipelago - and they had a rather good reputation - due to working hard. The logic and system was that a required workload was imposed on them - once the given task was done they were allowed "incentivized" to invested their "remaining" energy into paid extra labor or tasks.
It was the main reasons why many Asian slaves managed to buy their freedom within a rather short period and started to set up their own businesses (then only using Asian slaves - no Negros) to further their business.
Unfortunately Asian slaves across the board received the same miserable food and physical treatment as the Negros - that in majority had been brought in from Madagascar to the Cape Colony. Due to being from Africa the rate of runaways amongst African Negros was naturally far higher then that of the Asians.
A major part of the Negro slaves originated from the Cape area, mostly members of the Khoikhoi tribes and served in majority as domestics aka house-slaves. Due to their socio-cultural upbringing (pastoral tribes) they were naturally reluctant to engage in hard work and therefore were recognized to be unsuitable for manual farm or hard work, - thus the Dutch aka the VOC getting their slaves from their Asian colonies.
In contra Negros from the Ivory coast were known to be hard and skilled workers - due to being used to work as slaves on native plantations and being the backbone of the local run industry.
Slavery laws (treatment) were introduced into the Cape Colony in the 1820'ies and by 1838 Slavery had been abolished in South-Africa. The suppression of the Boers or Free Burghers via the English - led to the Great Trek, resulting in the new Boer Republics, Orange Free State in 1854 and the Zuid-Afrikaansche Republiek (ZAR), also known as the Transvaal in 1858.
Due to the abolishment of slavery - thus being replaced by paid workers - the Boers and the English hired Indian and Malay workers - thus rendering the Negros out of a job or even their basic existence - especially those pastoral Negro tribes that had been "robbed"of their land and cattle - foremost by the incoming Zulu nation since the 1750's.
The Negros that found employed, were in vast majority those of the Zulu nation - hard working and again having been used to work as slaves by their own chieftains, foremost in the agricultural/plantation industry - therefore they naturally appreciated free and paid work.
And many were able and willing to start up their own farms and plantations.
This history is what has led to the continued hatred (right-down mass killings) until today between members of the Zulu nation (incl. former Rhodesia) and those pastoral SA-Negros generally termed as Bantus. The latter foremost only found employment with the upcoming industrial revolution in SA from the 1900's onward. And members of the Zulu nation usually refuse (until today) to be common factory workers or e.g. miners.