The first point in which socialisation effects our dog's behaviour happens long before they move into our homes as either a rescue dog or puppy. It happens long before it 'is allowed out after first vaccinations'. The key point of socialisation is from 4 weeks old, when it is surrounded by litter mates and mum.
Many people underestimate this valuable time of life, and often put their own excitement of getting a new puppy before the welfare of the dog and ask to take it home sooner than 8 weeks. This is the primary problem with issues surrounding socialisation, those first 8 weeks, especially the later 4, are VITAL when teaching a dog about canine body language, communication and most importantly, confidence.
Playing with siblings, the weaning process with mum, where their sharp teeth cause her pain are all natural ways of teaching a puppy bite control. Mum teaches acceptable behaviour and litter mates signal when play gets too rough. Without this period of learning through play at such a young age, dogs will struggle to communicate with other dogs. They will always show some signs that their socialisation was limited at a younger age, and this will be costly in both time, effort and cost of extra training classes throughout the dogs adolescence.
When taking a puppy into your life, it is recommended they do not leave mum until 8 weeks old, in my professional opinion I would ask the breeder to hold until 10 weeks.