I would say that for a standard, or even a mini, probably OK. A toy, except to a very knowledgeable home preferably with other dogs, less so. 8, or even 6, weeks used to be the norm, but research and experience over the decades has shown how much pups benefit from continued play and experience with their mother and siblings. At the same time those very early months are the best time for the pup to learn not to fear all the sights and sounds of the big wide world, and not many breeders have the resources to socialise a large litter of big puppies as thoroughly as a dedicated owner working with just one puppy can. With tiny toy puppies the health risks are greater - they are at risk from hypoglycaemia and hyper/hypothermia, and the extra weeks can be essential. In these bizarre times many compromises have to be made, and if the breeder you have found ticks all the other boxes sending the pups to their new homes at 9 weeks would not be a deal breaker for me.