People are biased. There's no way around this, it's how our brains work. The scientific method helps to reduce, remove, and eliminate these biases by providing a framework for scientists to follow. Of particular importance is that there must be clear documentation of the steps taken when investigating and experimenting. This allows for peer-review, where others can follow those steps and confirm or overturn results and discoveries.
This also helps to unmask charlatans and tricksters, people who are deliberately deceiving others and promoting false information. It can take a while sometimes, but in the long run the garbage can be discarded and good results will remain.