A living wage is the minimum amount of money needed to meet basic needs, assuming someone does not have access to other means of support. Each adult is assumed to be paying for the needs of one child. No one is presumed to have a paid-off home or vacation condo, and no one is assumed to be paying off usurious debts. This amount of money is determined by the cost of living in a particular area. Last I heard, the estimated cost of living in the United States, in general, is about $37,000 a year. It will be more in urban or suburban areas, and less in rural areas. It will also vary by region. The east and west coats will cost more, the central parts of the country will cost less. Employers who pay less than the cost of living for full-time work in their area are pushing their labor costs off onto the public, who will be required to make up the difference through taxes for public-assistance programs. The question being addressed by the living wage/starvation wage division is not, what is sufficient for all circumstances, but, what is minimally necessary in common circumstances. Some people will have problems we'll need to help them with, like Sally. Others will have advantages which can help others out, like Bob. In general, I've found it pointless to speak about business practices in terms of ethics. Unfortunately, most business administrators and economists believe ethics to be unrelated to their practice. However, they will pay attention to utilitarian arguments. So, if you ask me a business question, I'll respond with a utilitarian argument. You can only speak about ethics to someone who is acquainted with the liberal arts.
I am not a business administrator or economist. I have a liberal arts degree. Utilitarian arguments are interesting, but I would like to explore the ethics of low-wage employment. I see I left out a feature of Alice and Bob's situation you need to know before answering my question. Let's say that the particular area they live in is average, so the cost of living is about $37,000 a year. Is their salary a living wage or a starvation wage?
Still probably a starvation wage, even though it might be easier to live on $37k in rural Alabama than in NYC. I base this mainly on the fact that wages are lowest in the Deep South, and (surprise, surprise) they also have the highest proportion of people on Medicaid and welfare. We can argue about the virtues and vices of free market economic all day, but the fact of the matter is that there is empirical evidence, the absolute, scientific gold standard of what actually happens in the world that shows that low wages are bad for everyone.