Researchers may impact what is said and done in the environment that they study; the mere presence of a researcher as well as the questions they ask, etc., may wield influence. In your opinion, how problematic is this concern?

Researchers may impact what is said and done in the environment that they study; the mere presence of a researcher as well as the questions they ask, etc., may wield influence. In your opinion, how problematic is this concern? What can/should be done to minimize this type of researcher influence?