Buying cabinetry is a big investment, so it pays to learn something about how they're built and what constitutes quality construction. First, look past the exterior to the interior, also called the box, to see from what material the backs and sides are made, and how they are joined together. Do this with the drawers as well.
Different types of doors attach differently to the cabinet boxes, which gives them different looks as well. Different door styles, of course, also help to create different design themes in the kitchen.
Industry standards for construction quality can help you get an idea of what to look for when shopping and what certification actually means.