An expert is an individual who, through training, education and experience has achieved a thorough understanding of all of the aspects concerning a particular field. They have a comprehensive working knowledge of the evidence that pertains to that field. The evidential aspect of expertise is extremely important, without evidence there can be no expertise as there is no standard to use to measure the individual's mastery of the information.
For example, someone might be able to formulate a very detailed, science based and persuading dissertation on the mating rituals and reproduction of the North American Skunk Ape (Bigfoot) but because there is not a shred of objective evidence the ape even exists, one can not be considered an expert in Bigfoot reproduction.
There is seemingly no end to the claims we encounter in our daily lives, many of them dealing with our own health or the health of our pets. To read the side bar ads on many websites we are constantly under attack from toxins, can make our muscles bigger if only we eat/take this one product and are missing out on saving some serious money by not using this insurance "trick." Of course we could be making that money from home if we just click the link on the video of the guy holding all that money. These claims are not validated by evidence and are not required to be. The first amendment comes with an expectation of due diligence on the citizen. Freedom comes with an inherent risk and is well worth the price. But a person making any claim like that can not be considered an expert.
There is no professional board or standard that a blogger on the internet, someone working in a pet store, training or grooming dogs and cats or even breeding animals is subject to. That's not to say that they can't be giving out good advice or that they haven't learned a lot through their experiences but it does not put them on equal footing with someone who's experience has been building on a solid foundation of traditional training and education anymore than my experiences with children and my medical knowledge would put me on equal footing with my daughters' pediatricians. For my children's health care, preventative and otherwise I rely on experts.
When I am approached by clients asking about latest fad diets, advice from people who work in the pet industry or alternatives to conventional medicines or conventional practices I often find myself explaining why I'm not willing to approach those issues from my position. I stand on a solid foundation of evidence based medical knowledge and my clients pay for and expect that expertise. When we venture away from the evidence and start to practice or recommend things based on our ideas or opinions, we are no longer the experts the public is relying on us to be. It is impossible to maintain any level of expertise absent evidence.
I'm not saying alternative medicine has nothing to offer. Nor would I discourage a client from investigating an alternative therapy for their pet. But my position is constant, if I can't find solid evidence that something works better than doing nothing or as good or better than the conventional therapy, I can not recommend it. To do so would undermine the reason I'm here in the first place. I would also be willing to go as far as to state that anyone offering that type of service or advice can not be considered an expert.