We only approve fixed dogs/cats. Are we supposed to exempt ESAs from this rule?

[Mila F.]

I have a young couple with a retriever puppy bombarding me with inquiries. I told them puppies and unfixed dogs would be a no-go for us. They said they don't plan on fixing the dog because they want to breed him (!!). Now they are saying they just registered the dog as ESA.  Obviously, ESA letter (if legitimate) gets them around the dog age, but what about spaying/neutering?  Is this legal of me to still require the ESA dog to be fixed?