One key element could be the power imbalance. Since she is 'purchased', the man may have more power initially. Another element might be the woman's reaction - whether she accepts her fate or tries to resist. Also, the social context that allows such a thing to happen (even if it's in a fictional or historical setting) is important.
The first key element is the act of 'purchase' itself. How does it occur? Is it a transaction in the open or a more covert deal? Then, there's the relationship between the so - called husband and wife. Is there any chance of love or understanding developing despite the unethical start? And finally, the external factors like the community's view on this situation. Do they condone it or oppose it?
In the story of'my purchased wife', a significant element is the origin of the woman being sold. Is it due to poverty, family pressure, or some other reason? The expectations of the 'purchaser' are also key. Does he expect a submissive servant or a true partner? And the woman's journey towards self - discovery and empowerment within this constrained situation is an important aspect as well. She might gradually realize her own worth and fight for her rights.