I am looking at a puppy's pedigree and the maternal and paternal grandmother is the same bitch.
Would you be in any way concerned and are there any  questions I should be asking the breeder with this in mind ?
Thanks in advance.

You mean the parents are half brother and half sister? It wouldn't worry me but I'd like to know why, as it's a mating you'd only do for good reasons, something to think twice about, something you'd do when you were after a particular quality, and the breeder would need to know the dogs behind in more detail. I've done it myself but it's not something I'd ever do without a lot of careful thought as it doesn't always work out. I got some great qualities in my pups but did also end up with one unexpected problem -two pups had one missing testicle each.

My youngest homebred bitch champion has such a pedigree, this is a half brother to half sister mating, which is as close as I would ever go.

I would want to know the reasoning behind choosing to mate these two.

In my case both parents were by imported stud dogs were outcrosses unrelated to the bitch, who was the type I want to maintain. 

The bitch from her first litter is very nice (who also became a champion) was then also mated to a foreign outcross, and even though it expanded the gene pool I was in danger of loosing some of the good traits of the original bitch, and the bitch I kept is nothign special as the quality was in the males.

For her second litter I decided to use her half brother as unfortunately his sire had missed to her (he was 9 years old), but had produced to her mother.

I knew going so close would hopefully stabilise the type I wanted to retain, but that I would be forced to outcross in the next generation, which I have done.

Thanks for your replies.
Puppy was considerably more than I was expecting to pay so it was a no from me !