Hi
He needs to draw up a contract stating that they are not to be used for breeding and he can withold papers until proof of neutering has been recieved from vet so either a letter from them or I have done my own stating that the individual kitten in question was neutered on such and such a date etc and this then gets posted out to me. That is providing the mother is a registered pedigree ofcourse, if not then that wont really work. Most people would be put of it they dont have a pedigree as if they are wanting to breed for money then they wont get much if they are not registered, but it does not stop them doing so if they really want to. Other than getting the cats altered before sale theres not much you can do but it is definately worth having a contract otherwise he wont have a leg to stand on if someone does breed against his wishes. see my website and click on kitten contract on bottom of adopting a kitten page to see an example of what to write in one.
http://www.druzhinasiberians.co.uk
Clare