As a LDS owner, here are a few things you should know about buying from your LDS.
We assemble and test all equipment with the customer. We walk through all equipment and show the customer how all the functions work. If there is a problem, they fix it on the spot. If it is major, it is replaced immediately. If it needs to be returned to the manufacturer, we provide a "loaner" free of charge until yours comes back.
The customers who support the store, and the more they buy, they get free rentals, free air, discounted nitrox, discounts on trips and classes, and occassionally, a free boat charter. The more you buy, the more likely you will get steeper discounts on future purchases.
We don't like to "wheel and deal". This isn't a used car lot. However, most LDS will meet or beat any internet discount that comes from a authorized dealer. Our philosophy is simple. We offer a good price and outstanding service. Any LDS who doesn't provide this service will not be in business.
As many posters have stated, there are a lot of reasons to pay the extra and support your LDS. I would agree, but only if you feel they are supporting you to dive. Ask these questions...are they inviting you to dive with them on shop dive night? Are they inviting you to activities or classes the shop offers? Are they wanting you to come on trips with them? If the answer is yes, then you will see the extra you spend come back to you. If not, you may as well go shop on line.