The field is not like a laboratory. There are no control conditions, so that the work done can be seen as part science and part art. There is a part which is subjective and a part which is objective. Weight and height. Surveys people can lie.
Subjectivity can also depend on ones gender.
Different individuals can bring different visions and backgrounds to fieldwork. The Trobinand Islanders. Malinowski did fieldwork in the 1920's and Annette Weiner restudied these people in the 1960's. Both had a different perspective and understanding of the economic system of these people. Subjectivity is not wrong.