Did blacks sell blacks?
Answer: yes.
I will give you a truly remarkable example.
In the 1930s the True Whig Party – a party composed almost exclusively of the descendants of freed American slaves – sold hundreds of Africans to the island of Fernando Po. They also voted to reinstitute the institution of forced (indentured) labour.
This was more than a century after the abolition of slavery in England.
Let that sink in.