I probably shouldn't have answered so simply, lol.
But currently there is no federally recognized certification or registry of any kind. It doesn't matter what a place claims, what they're offering (selling) is meaningless and they're in it for the money. Federal law does not require any certification or registration for service dogs. To implement such a thing is an incredibly huge undertaking with many problems that limits the current civil rights of individuals with disabilities. Solving that problem as well as financing such a thing has not yet been done.