Anyways they were whipped (there were other weapons too) if they didn' work as much as the owners wanted and they were given very little food for the amount of labor they did.
Buy them at a slave auction, or hire somone to capture a runaway one.
Cheap (free) labor, and it wasn't illegal at the time. The free market spoke.
To grow and pick cotton.
because they can do the works for the slave owner
Because they felt like it.