@Zergio200ism the term of slaves is fully depended on the law of county/world. 
and the state allows slavery. 
 slavery are commonly 2 types. debt slaves and criminal slaves.
1 is a punishment. the other is when someone can no longer support them self.
being able to put on conditions might be a rule of sort. 
slaves are in fact a product. dus having the product in good condition,  means they are more worth. that is what the ''honest trades go by''
the illegal ones, profit by kidnapping. 
there is only a few reasons why a slave is abused. 
1 is when a slave is de-humanized.  meaning they are treated as lesser being, and to boost ego/superiority of the one abusing.
2 punishment/training/breaking someones will.