When young women in developing countries, or young women with limited means in wealthy countries, enter sexual relationships, they often do so not solely for sexual and emotional benefits, but also with expectations of material advantage. This makes the dynamics relatively straightforward.
Ideally, from the perspective of the young woman and her family, this material advantage is provided lifelong and guaranteed by a legal system, as in a formal marriage.
Short of that, if a wealthy man is not available for that degree of commitment, arrangements can be temporary. It is still an exchange of a sexual relationship for economic benefits.
Judgments on morality often merely reflect the judges' own sexual and economic interests.
A man who later becomes the woman’s husband might, if he were to know, find a premarital affair immoral. He may feel "overcharged" because he has to enter a formal marriage to secure sexual benefits, while the previous partner only had to provide temporary support.
Men with fewer financial means will also often denounce such behavior as immoral. Lacking the means, they may oppose arrangements they themselves cannot afford.
Some of her female friends might defend her decision, particularly those who would consider such an arrangement for themselves.
Conversely, less physically attractive female friends might criticize her attitude, feeling that such an opportunity is unlikely to come their way.
People’s opinions often merely disguise their underlying interests.
Can the behavior of a young woman who agrees to a sexual relationship because she expects material benefits be classified as prostitution?
Colloquially, often not. Commercial prostitution typically involves the exchange of sexual services for financial remuneration on a highly promiscuous basis (e.g., multiple clients in a short period) and in an indiscriminate manner (accepting any client who pays the requested price), whereas long-term transactional arrangements are generally viewed differently in social contexts.