My puppies don't totally wean from the Mom until 8 or 9 weeks of age.  No puppy ever goes to a new home less than 12 weeks and most often 4 months. 
Buying them less than 12 weeks is risky.  I got a phone call yesterday afternoon from someone that bought a pup less than 8 weeks through the paper.  They were having problems and the Vet they went to knew less than they did to help this puppy.   
I told them what to do and which clinic to go to if the problems persist as they could lose that pup.  Hope it worked out for them.        |