How is the economy likely to be affected if a democracy becomes an oligarchy ?

The answer to this question is: Upper classes in power are likely to become richer at the expense of others

In Oligarchy, the government will be fully centralized and totally controlled by the upper class of the society. This means that all legislation that made by the government will be very likely to bring benefit for themselves first rather than paying attention to the things that the majority of citizens need the msot.