I took her comment as she wouldn't purchase a puppy that was raised as a singleton. This pup wasn't. Most breeders, if they have a singleton, will move heaven and earth to make sure that the pup is given the correct environment to NOT have the issues of being a single pup. They do as this breeder did. Or bring in other pups in some other way once the pup is up and around to insure that the dog is properly socialized.
Yes, a breeder who didn't do (or didn't know to do) these things would be one to be avoided. Your argument is like saying "I know someone who had all the health tests and still ended up with issues. So no reason to worry about the breeder doing hips/elbows" It's about stacking the odds in your favor
When Wolfy-dog made her comment, she did not know that the pup would not be raised as a singleton. It is like we immediately try to figure out reasons why someone should not buy the pup they picked out. It really is bursting one's bubble, considering the work in finding a breeder, then waiting for your pup to be born and out of the woods, and be being so excited to get a picture of the puppy. And then we say, "oh it's a singleton" or whatever other thing comes to mind to make someone question whether their choice is a good one.
The problem with what you are saying about most breeders is that it is simply not true. Most breeders do not have multiple litters on the ground of precisely the same age, and hopefully the same breed. For example, you would not raise a shepherd puppy with Yorkie puppies. They would have to be the same age and the same breed or at lest one of similar size and strength. Even a week's difference will make the older pup or puppies so much stronger and tougher that the younger puppies might be injured by bullying. So a breeder would have to have two bitches come into season on practically the same day, whelp two litters within a week of each other to have puppies that could be put together like you say.
As for moving Heaven and Earth to bring in other puppies of those ages to properly socialize a puppy, sorry but no. Most breeders are not going to upset their dam and litter to socialize another breeder's litter of one, and possibly introduce diseases. And no, there aren't vaccines for all the diseases that can kill baby-puppies. So until they are about 4 weeks old at least, there will be no interaction. And even then, I know there is no parvo on my place, but do I trust the breeder down the road? No. No, I am not going to lend a couple of 4 week old puppies out to some other breeder to help socialize their singleton. And I would say most breeders would feel that way.
As for putting in puppies that are say a week or a couple of weeks different to get that socialization that we are all fired up worried about, if the puppy is younger, it will learn all the wrong things from the other puppies. I did have a singleton once besides cupcake who had no issues that Wolfy-dog was talking about, but our concern with her was keeping her alive and getting her up to weight. The other single pup was born 3 weeks after a litter of 9 puppies. Having all 10 nozzles he grew at an enormous rate, and by the time he was walking with his eyes open, and good control of both -- 3 weeks, the other pups were 6 weeks old. And he was about as big as they were.
I put him in with them, just when I could supervise, and Bear was not thrilled with him being there but she tolerated him. The other pups were older, but not bigger, still the advantage was with the older puppies. I let them play together and carefully supervised.
Frankly, to have an outside breeder do this, you would have to be best of friends, and really, even if two best friends had litters days apart, a best friend would probably not ask a best friend to put her pups in jeopardy.
And, of course, having multiple litters at the same time, is probably something that most of knowledgeable folks here would frown on and try to make you question your breeder about. Not that there is anything wrong with having a couple of litters on the ground at the same time. But that is what the folks on this site do.
Dainnera, have you had a litter with a singleton puppy, and did you find a neighboring breeder that was willing to let you swap puppies or integrate into their litter?