Thats what I question. Just because he doesn't have testicles, just means he may by chryptorchid and just not like a normal active stud.
To test a true Hermi, parts of the inner female parts need to be tested to see if they are ovarian material or male testes.
Have worked at vets for over 35 years, and I can truly say I have seen one true Hermie, it was a dog with male sheath, not real normal, but overies and uterous inside. We started to neuter, then ended up spaying instead.
I believe this is just another scammer trying to make money. Would be fun to actually email and ask for veterinarian confirmation on the hermi diagnosis..