How do you do this and how much do they cost?

To all who reply thanks frank.

Nothing you place them when you register your puppies, or if it is an older dog (as long as it is in your physical ownership and posesion) you write to the kennel club to have one or both endorsemetns included.

It is easiest to endorse a whole litter and then remove them later if appropriate.  The pups I keep still get endorsed, the only two I never did were ones that were going to freinds abroad.

In addition to what brainless has said it doesnt cost anything to do :)

to add on to what the others have said you must be aware they are onkly valid if you can present a signed copy of a agreement between you and the purchaser showing they were aware the endorsement was in place at the time of purchase

IE a puppy sales contract! do a search on here theres lots of info on them :)

Yes most important, and the Kennel Club remind you of this when they send the regitrations back.

I actually 100% agree with this.  I got caught by this with my first dally.  The lady sold her to me and did not tell me she had endorsed her pedigree even on the pedigree she gave me there was a clause for special conditions.  I had my first litter and found out she had done this when the registrations come back from the KC.  She did release it which was just as well as I had sold all the pups.  I would not have minded had she explained to me but she didnt and I just thought it was a bit sneaky especially as unless you are looking for it you wouldnt notice it.  I have never once had someone refuse one of my dogs when they see the reasons behind it and also get them to sign a contract.