Does it follow that I reject all authority? Far from me such a thought. In the matter of boots, I refer to the authority of the bootmaker; concerning houses, canals, or railroads, I consult that of the architect or engineer. For such or such special knowledge I apply to such or such a savant. But I allow neither the bootmaker nor the architect nor the savant to impose his authority upon me. I listen to them freely and with all the respect merited by their intelligence, their character, their knowledge, reserving always my incontestable right of criticism censure. I do not content myself with consulting authority in any special branch; I consult several; I compare their opinions, and choose that which seems to me the soundest. But I recognize no infallible authority, even in special questions; consequently, whatever respect I may have for the honesty and the sincerity of such or such an individual, I have no absolute faith in any person. Such a faith would be fatal to my reason, to my liberty, and even to the success of my undertakings; it would immediately transform me into a stupid slave, an instrument of the will and interests of others.

— Mikhail Bakunin, God and the state, Chapter 2

Expertise merely refers to one’s knowledge or skill in a particular field, but my understanding of CPR or ability to bake shortbread cookies does not make me an authority over you. Other than the conflation of force and authority, this is one of the most common confusions people have about anarchism, made worse by the fact that there are some anarchists who still use authority to refer to both command and expertise just because Bakunin did. Personally, I find that creates needless confusion. If you’re using the word authority to describe everything from slavery to knowing how to build a bridge, then why use the word at all? Just use the word expertise when you’re talking about expertise. Listening to medical advice isn’t a hierarchy. Having expertise doesn’t give me the right to command you unless I hold a position in a hierarchical power structure that grants me that authority. As Bakunin himself said:

...we ask nothing better than to see men endowed with great knowledge, great experience, great minds, and, above all, great hearts, exert over us a natural and legitimate influence, freely accepted and never imposed in the name of any official authority whatsoever, celestial or terrestrial.

— Andrewism, How Anarchy Works » Dissecting Authority (https://www.youtube.com/watch?v=lrTzjaXskUU)