What dog breeders have been advocating for years is, to me, the best way to go. Only allow licensed kennels to breed and/or sell dogs,. nobody else.
I have been involved with dogs all my life, both breeding and showing, and if we [my Mother and I] didn't like the cut of the jib of the person who wanted to purchase a puppy, then he/she didn't get to buy one.
Responsible breeders only sell to responsible people.
G.