
If the breeder takes the care to socialise the pups properly there should be no problem. check that they will have been exposed to the sight and sound of traffic, been for rides in the car, seen all kinds of people etc. If I was getting a Puppy from someone I trusted could do all these things with all the pups in the litter, then it doesn't matter what age you got him, as he should be well adjusted.
I think this advice is often given due to the fact that many people that 'produce' puppies will not have made such an effort, but then they would also be unlikely to want to keep them that long, as they would want to bank the money as quickly as possible!
Unfortunately it is sometimes the case that some breeders will not do enough socialisation, but you still have time before the sensitive phase, and if the pups at 10 weeks are lively fearless and friendly, I wouldn't worry. My first two dogs were this age when I got them, one due to me moving house, and the other had just not been sold yet! The first belonged to a breed that needs a lot of socialisation, as they are suspicious and wary of strangers, and the other was my current breed. The first was no more difficult to socialise to things than I would expect for her breed, the latter no bother at all.
I would question the breeder as to her socialisation plan for the pups!!
I exported a Puppy to Australia, where on arival it would have to do a months quarantine. It went at 14 1/2 weeks, which meant it was 19 weeks when it came out of quarantine. it came out on Easter Monday, and the following saturday won Best Baby Puppy in show.
BUT from 6 weeks old I had carried her around in a Holdall, to School on errands, visiting friends (the dog owning ones dogs were vaccinated), going on Bus and car rides etc! she was also pretty well housetrained! It was extremely hard letting her go. the owners have found her veryt self assured, and I put this down to the socialisation she received.
On the other hand when the new owners of another Puppy did not socialise their Pup well with other dogs, in a Country home, this Pup didn't like large gatherings of people and dogs, but loved Horse Shows, as she lived with Pony owners and Exhibitors!