When buying an air conditioner, it is important to consider several factors such as the type of air conditioner (window, split, portable, etc.), energy efficiency, noise level, and maintenance requirements. It is recommended to choose a model that suits your budget and cooling needs, and to read reviews from reputable sources before making a purchase. Additionally, it is important to consider the warranty offered by the seller and the ease of installation. Online retailers may offer more extensive catalogues of air conditioners than physical stores, but it is essential to check the returns policy and customer reviews before making a purchase.