Socialisation has a deadline, and handling practice has to start before anyone needs it.
Between roughly three and sixteen weeks a puppy decides what counts as normal. A puppy who has had their paws held, ears looked in and mouth opened at home — for a treat, ten seconds at a time — becomes a dog we can examine without restraint at eight years old.
The plan is unglamorous: paws on Monday, ears on Tuesday, mouth on Wednesday, nothing on Thursday. Two minutes a day. Bring them in for a weigh-and-a-biscuit visit with no examination at all, so the building stops predicting anything unpleasant.