Faulty Goods: The Basics
Some basics to start with:
The contract is between the purchaser and whoever you make payment to. So for example if you buy a gift for someone you are the one who has made the contract and if subsequently there is a problem you would have to return to the shop and seek redress. (The only way round this would be if you were able to give the name of whoever you were buying the present for to the seller e.g. on the guarantee). It also follows that it is the place that accepted your money that your contract is with. You should not be put off by someone in the shop who says "it's not our problem contact the manufacturer".
It is also worth remembering that you have fewer rights when buying from a private individual. When buying from an individual your only right is that the goods should match their description.