West Highland White Terrier Breed Standard - The Kennel Club
Hate to break it to you but based on the breed standard, your "West Highland White Terrier" looks like a cross (maybe with a maltese?) to me. Is not as strong, sturdy or rough coated as other westies I've seen.
He is very cute, enjoy. But I wouldn't recommend that pet shop / puppy mill if I was you. If you do want a pure bred puppy from a breeder who cares about the health of their breed - you will have to wait. They will always get potential and patient buyers in advance, they will have waiting lists. Or they won't breed their dogs. They have no interest in encouraging impulse buys or people have no patience. Not good qualities in dog owners.
It took me a year and a half to find the right dog for me from the shelter and she was worth the wait.