Hi, I am on a breeders waiting list for a puppy.  The breeder was recommended to me and I have  met him at various shows last year and is not a puppy farmer. I have been told that the mating is  granddaughter to grandson.  Is this usual to breed such close relatives?   I am not very knowledgeable on breeding matters but have owned dogs before. 
Should I go ahead?  Your advice would be very much appreciated. 
Thank you.

Do you mean Grandmother to Grandson?  I'm trying to get my head round Granddaughter to Grandson ......

Have you checked the CoI on the kennel club website to give you an idea how close the mating is in reality.

Sounds like the parents are cousins

That was the only possibility my brain could come up with

I meant to say GrandMOTHER to Grandson!

> I have been told that the mating is granddaughter to grandson

In a lot of dogs pedigrees you will see recurring grandparents, g.g. parents etc, and that's fine if all else has been considered. If you never had any recurring ancestors dogs would not look like a particular breed or type. So I wouldn't worry about that one mating, I would check out the COI on the KC website and I would ask the breeder about dogs that are doubled up on, the good and the bad points, but no, I wouldn't worry about that.

Edited to say here's an example of such a mating, grandson and grandaughter of Kristull Unbreakable, this mating actually has a below average COI.