Bottom line, the salesclerk is not diving the gear, you are. So be sure you like how it fits, feels and looks on you. Rememer function over form and you need to be happy. Normal dive position is horizontal not verticle and it needs to fit you well.
Do make an effort to try the blackplate and wing before you buy. The modular design and comfort are worth it. Cost is about the same for a BCD, but IMHO will serve you better and longer. Deep Sea Supply (DSS) Backplate and wing (BW) are great. Open in front with just webing over the shoulders and around the waist so it works well for any bodytype or gender. Blackplates come in tall, short, medium and the wing is selected based on the weight you wear and the number of tanks you plan to wear. The tank is anchored to a metal plate that is about as wide as your back giving you a stable platform for the tank (BCDs often have a narrow piece of plastic with the tank balancing on top and the cloth trying to hold it stable, or at best a small triangular shaped piece of plastic).