"Alsatian" and GSD" are just different names for the same breed......honestly, he doesn't really look like a GSD to me. Too small, from what I can see. He also doesn't look too healthy . What breed is he supposed to be? (what are the sellers calling him?)
The puppy you buy doesn't have to be a purebred to be healthy.
Is there a shelter where you live from where you could possibly adopt a dog? If so, I advise you to do that rather then giving business to people who don't take proper care of their pups.
If he's "purebred" then he's a poor example. Most white GSD's have black noses...as having a pink nose is a disqualifying fault.
How old is he? He looks lean and wormy to me (pot belly usually equals wormy) he also looks to be kept in crappy conditions and isn't clean at all. I know keeping white clean is a hard task, but seriously, why buy from someone who can't be bothered to bathe the dog for photos if they are truly intending on selling? Looks shady to me.