Purchasing equipment for scuba diving is a large commitment. Most quality gear is not inexpensive, and like any tool, you generally get what you pay for. When you compare the price of equipment today to what the same equipment cost 30 years ago, it is a much better value. Brick and mortar diveshops are the backbone of the scuba industry. While it is possible to find equipment online for a slightly lower price, the total cost of ownership is actually lower if purchased through your shop.
Your dive shop will ask questions when you come in to look at equipment. Those questions will help them to assist you in selecting what is right for you. Along with the professional help, you can try on the items to ensure proper fit. You can touch and feel the quality, and even be put in touch with others that have used that type of equipment to see how it performs.
Dive shops will assemble, and test your equipment when you purchase it. Dive shop personnel know their customers, and keep records of service. Most manufacturers offer service programs through your shop, which lowers total ownership costs.
Most shops offer diving opportunities, and advise on diving and conditions of the dive sites. They provide airfills, equipment adjustments, and dive buddies. They rent equipment that maybe you only need form time to time, or just aren't ready to purchase yet. All of these things add up to value far beyond the initial purchase.