At the risk of preaching- please don't buy a dog from a pet shop. If you are a responsible person who genuinely care about animals you will not want to be encouraging the awful animal trade that goes on. Often these puppies are taken away from their mothers far too early causing health and emotional problems. Even if the animal looks healthy enough they often go on to develop many problems. I urge you to wait and see if you can get the dog you desire from one of the rescue places or alternatively get in touch with a breeder. That way you can get a look at the mum, see how they interact and have some idea of medical history. Getting a dog is always a gamble, you never know quite what you are going to get but you wouln't want to take unnecessary risk. I know this has turned into a bit of a lecture but I have had a bad experience of dogs coming from "puppy farms", that is where the pet shops get them from. These dogs are often ill treated, badly fed, un vaccinated, badly bred, and over bred- have puppies continuosly.

Why not pop into a dog rescue place and see if anything takes your fancy? it's funny how you can be swayed once you meet the dogs and see their personalities.
I hope you find the dog you are looking for