Is there just a single "way of knowing?" Call it "the scientific method." Or are there various ways of coming to reliable knowledge of the world? Certainly each scientist works a bit differently. No two work in exactly the same way. Methods and standards also vary from one field to the next. Theoreticians may work differently from experimentalists. Deduction and induction.
The extent of human knowledge far surpasses what can be mastered by a single individual. It would take more than a dozen good scientists to master physics alone. So one has to trust in "authorities." You can't possibly do all the experimental tests yourself. You can't possibly check all of the math proofs.