I'd just tell your friend you want to hold off for now, and that he probably ought to get the puppy tested and checked at his own vet. I don't know if there's any way to tell whether he actually has or has not received the appropriate shots, but it'd be a good idea to have a vet look him over. He's going to want to have a good vet for the dog anyway, so he might as well establish one right off the bat.

I don't know that much about parvo beyond what I've seen on animal planet, but that's the kind of thing I'd be really paranoid about too. I'm always worried about feline leukemia or feline HIV with my cat, even though it's much less contagious than something like parvo.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)