I think we need to specify who we mean when we say "Africans." The victims, or losers in the Atlantic slave trade were not all Africans. Many African political leaders profited quite handsomely from a trade they in many ways controlled, and, at least until the late eighteenth century, conducted on their own terms. To quote historian Philip Morgan:
Resistance to the trade is dramatic evidence of African agency, but it was exceptional; better testimony to the upper hand that Africans established...is the way in which the terms of trade shifted inexorably in their favor...Not only did they secure better prices for their slaves over time, they also increased port charges, customary tributes, and other fees...At least before the early nineteenth century (when British-imposed abolition began to curtail demand), the Atlantic slave trade was largely a sellers' market.
So not all Africans were victims, or losers in the slave trade. It is important to note here, though, that Africans were not generally "selling their own people" but rather people from often distant, interior lands with whom they felt little or no solidarity. In addition, slave merchants in European ports, especially Liverpool and Bristol in the eighteenth century after Britain gained a monopoly on the trade, profited immensely from it. At risk of oversimplifying a very complex system, the slave trade generated enormous wealth in Africa, the Americas, and Europe, but at the end of the day it was based on the labor of the African slaves (not to overlook the legions of indentured white laborers) and in this sense I completely agree with the previous answer. But it is important to think about who we mean when we say "Africans."
Source: Philip D. Morgan, "Africa and the Atlantic, c. 1450 to c. 1820" in Morgan and Jack P. Green, eds., The Atlantic World: A Critical Appraisal (New York: Oxford University Press, 2009), 228-229.