Slave trading was not very popular until later in Ancient Egypt. Only slaves with special traits were traded worldwide. Slaves with a special skill were more valuable than those without one.
Slaves had plenty of jobs that they could be assigned to.
Most philosophers of classical antiquity defended slavery as a natural and necessary institution.
Aristotle believed that the practice of any manual or banausic job should disqualify the practitioner from citizenship.
Greek slaves had some opportunities for emancipation, though all of these came at some cost to their masters.