Regarding experts- they understand they don't know everything. Experts are constant foragers of information. So continually read up on subject matter, get a variety of sources. If your expert knowledge only comes from one source, say Wikipedia, that is not a very broad range. Learning about conflicting viewpoints, counter-arguments, and other challenges can solidify your knowledge base.
Being challenged isn't attacking credibility. It's strengthening the foundation. And it also exposes gaps in your knowledge base, providing room for improvement.
So the main points:
1. Gather information from many sources
2. Know the challenges within your subject matter
3. Test the information to ensure it is accurate and reliable