There are some possible ways to try to decide which of the ethnographers is right, but it is also true that neither of them must necessarily be right or wrong. Ethnography is nothing like an exact science. Ethnography consists of human beings, with their own points of view, opinions, and prejudices, trying to make sense of something as complex as a society. There is no way to objectively measure and describe most aspects of society and culture.
In this hypothetical, we could start by looking at the two ethnographers’ research methods. It could be that one of them has conducted their research poorly. For example, imagine if a researcher concluded that men hold all the power in a culture, but based that conclusion on observation and discussions with men. Now imagine that another researcher also talked to women and children in that society. We would be justified in suspecting that the first account might be less reliable.
Secondly, we could examine what we know of the ethnographers’ own backgrounds and attitudes. An ethnographer who was, for example, politically active in anti-globalization work might be more likely to find that the culture being studied is under pressure from outside influences. We have to keep in mind that scholars’ prejudices and attitudes can affect their findings.
Fundamentally, however, neither scholar must necessarily be “right” or “wrong.” These words may not even make sense when applied to ethnography. The two views of the society can simply be seen as the result of the fact that human society is complex and can appear very different to people with different experiences and different points of view.