I have faced a similar problem myself while looking for a Chihuahua. Although Ive been told I wont get a pup because Im in the UK on a working visa and 'what will happen to the pup when you go home'. Not that it is anyones business really.
But I intend to stay on once my visa has expired as my fiancee is a citizen here, and its becoming very tiresome having to explain this and share personal information about my status here with breeders for them to even speak to me, then only to have them, in most cases, start asking me personal questions about my relationship so they can decide if I am really going to stay on or if I am bsing them at which point, depending on my mood I usually tell them that details of my relationship has nothing to do with my ability to provide a good home for a puppy, or I tell them to mind their own business. Because honestly that information is personal, and along with my status here should only be shared with immigration and my employer / potential employers. And regardless of all that, should I ever go home the dog would come with me.
Honestly the way I have been spoken to and the things said to me. Ive been told that Im just one of 'those' people who will throw the dog away when it comes time to go home etc. Which is extremely presumptious and RUDE. Ive been called all manner of names as well because of my accent and its not something I would have expected to deal with, or have to deal with, when looking for a puppy.
In my situation BYBs and farmers treat me better when I call up - not that I knowingly called them, I called, then went to see pups when I realised what kinds of operations these people were running.
I have no intention of buying a pup from one of these places, but I can immagine others in my situation doing so, even if only because of the treatment they have received from reputable breeders. But at this rate it looks like I wont get a pup from a decent breeder without providing copies of my visas and all kinds of other rubish - something that I was actually ASKED for!!!