My vote is don't breed or buy or even rescue any pups at all - ever. Sorry to be harsh, but someone who was willing to give up a puppy because he MIGHT be 10lbs versus 5 is not fit to own even one, in my opinion. Does this ring a bell?
http://www.yorkietalk.com/forums/gre...y-new-pup.html
Honestly, if you could consider selling a pup due to size, what's to stop you from abandoning a rescue pup that doesn't meet your coloring expectations, or personality wishes?