how old can a puppy be before being able to leave the mom to be sold

no earlier than 8 weeks. some breeders won’t let them go until 12 weeks.

I’d go with 12 weeks. Some get behavior issued if taken away earlier.

I have two labrador retrievers and got both of them when they were 8 weeks old. I think that is the appropriate age to take them away from their mom/litter mates. neither of them had any huge issues as puppies and they are wonderful dogs.

between 9 and 12 weeks and depending on a breed too. Smaller breed needs more time with their mommy

As soon as they drink milk by themselves… they are good to go.