The most prolific slave traders in all of human history were Arab Muslims, with the practice reaching its height under the Ottoman empire. Their total slave trade far exceeded that of the British, Portuguese and Spanish empires combined by several hundred percent according to most estimates.
The highest number of slaves per capita in any population was none other than Mauritania, also the last country to officially ban the practice as late as 1909.
It is still really common in Islamic countries for the wealthy to "hire" black men in particular to oversee their households. Yet even the hired help still live under incredibly austere conditions, earning the rough equivalent of perhaps $150 to $200 per month on the high end- and that would be in the "wealthier" countries.
The actual Berbers of the Greater Atlas are actually the only people in the region who were never fully conquered by the expansion of the Islamic empire- mostly because of their lack of any real resources and the remoteness of where they live. I've done bartering and trading with them (mountain Berbers), and they have the most peculiar- and completely unique written language, unlike anything else in all of Africa or the Middle East. The written form is still used among the roaming Touareg- the descendents of some of the original Berbers. I've read that specialists believe the language goes back to before the Punic wars.