Some have argued that beer was the foundation of civilization. I would suggest slavery could equally claim that title. There are records of slavery as an established institution throughout all recorded history which implies that it predates history. In the ignorance of the uneducated it is tempting to promote the idea that slavery was the invention of the white people. Or of even the Europeans. But that is a false claim. Some slaves could travel to other nations, and were entrusted to conduct their duties with minimal supervision. Some had great authority over large groups of people and in some cases nations. Other slaves merely unskilled laborers. The answer to your question relies on what the slave did, and how well trusted he or she was. Some slaves had great wealth and personal property and political and military power, and yes, other slaves. Other slaves were treated like beasts of burden. So to answer your question yes, some were entrusted to come and go. Others either proved they could not be trusted or never got the chance to prove their trustworthiness.