To be clear - I would buy fins that I tried on and swam with from my LDS. Being able to try things on is the advantage of purchasing through an LDS. I do not believe in using my LDS as a "fitting room" and then ordering the product online. We just paid through the nose to purchase a new BCD for my divebuddy at a LDS. We could have confirmed the size and then ordered online, but that's not cricket. I am willing to pay a premium for service that an online supplier can not provide.
But: I just received a dive light in the mail the other day. None of my LDS stocked the brand / model I wanted (LDS == limited selection). I knew the light and it was on deep discount clearance sale online. It cost less than 50% of buying a comparable light at a LDS.