A bright, warm and sheltered location
Poinsettias need light to thrive. They don't like cold and draughts. In a shop, plants should be placed in a bright, warm spot protected from draughts. Steer clear of poinsettias displayed in a draughty entrance area or outdoors in windy conditions and temperatures below 15°C, or in a dark corner of the shop. They may have suffered damage that will only become visible a week later when the leaves drop.
The right amount of water
Poinsettias shouldn't be allowed to dry out completely or become soggy. Too much water in particular can cause lasting damage to the plants. It's easy to check whether a poinsettia is getting the right amount of water: Simply lift the plant and its pot a little. If it's very light or noticeably heavy, be wary of buying it. The plant should also not be standing in water. If in doubt, choose a different poinsettia.
Well protected on the way home
To ensure your poinsettias survive the journey to their new home unscathed in winter weather, they need to be well packed for transport. Specialist retailers should be well-eqipped for this and have the necessary packaging materials in store, such as paper to wrap your plant in.