Honestly, I have been less impressed with some of the professional services out there than I have with a few individuals who, while not professionals, have nonetheless done a great deal of 'amateur' education for their own interest and who have hands-on experience with challenging dogs.
Amateur does not mean necessarily unqualified or uneducated. Some 'amateur' dog owners/care providers I have met have a breadth and depth of knowledge and experience that would put some of the folks with professional certification that I have met to shame.
There are both professional and amateur skilled, trustworthy, knowledgeable, reliable sitters. And there are both professional and amateur sitters I would not trust with my dogs.
Key is sorting through the haystack to find the needle.
Be it amateur or professional.
Several of the professional services I have interviewed base their business model on caring for many dogs at once, which means that less attention can be given to an individual dog. This means expecting the dog to just slot in with an ever changing pack, expecting good social behavior from each dog without too much management on their part.
Not all are set up this way, certainly. But as one-one management is more cost intensive than what the general market will bear, some professional services rely on large numbers to make up for lower per dog costs. Many of these will not take a dog who has 'issues'.
Of course the amateur who takes in dogs without understanding the responsibility, without solid knowledge of how to handle a challenging dog, is the worst of both worlds.
If you need one-to-one care for a challenging or 'special needs' dog, you likely will have to search long and hard for the right person. Don't discount any avenue in your search, but do be prepared to interview many dozens of candidates, amateurs and professionals alike, to find the right person. And be prepared to invest time in trial walks and care situations so that you can assess if the person you choose is truly a good fit for your dog.
Again, wishing you all the best.
(To be clear: An 'amateur' dog care provider still must have done the SKN courses - the same courses that dog owners must do.)