I have ordered from quite a few on-line retailers who sell live fish. I am very impressed with liveaquaria, blue zoo aquatics, and vivid aquariums. I have ordered from these on-line retailers multiple times and have always had good experiences. Prices on-line are often much less than through a brick and motar retailer even when considering the cost of shiping, particularlly when you purchase multiple items to spread the shiping costs and that you oten are not charged state sales tax.
I am not overly impressed with Reef Hot Spot. I have had several fish arrive dead, and the thing I really do not like about them is if you place an order for a bunch of fish they will ship your order without one of the fish because it is out of stock or does not look healthy and not even tell you before they ship the order. As such, if you order two fish, one fish which is expensive and another cheap fish you order just to take advantage of the shiping, they will ship you just the cheap fish and not the expensive one when the expensive one is out of stock or not healthy without checking with you first. In such a situation, most people would cancel the order or at least put he order on hold because the shiping is too expensive for just the one cheap fish.
You need to careful because there are a bunch of very shady on-line livestock sellers which sell very sick livestock, often ship the wrong livestock, and are known for not doing business in a very honest fashion. As such, you are much safer dealing with established companies who have great reputations like the ones I listed above.
Overall, unless you are lucky enough to have an LFS which is very good and reasonably priced (which is, as stated above, a very rare commodity these days), you are usually better off buying livestock on-line because of the guarantee you get (which is usually never available when purchasing locally), and the quality and health of the livestock available on-line. People are often put off from buying livestock on-line because they feel that the shiping is very hard on the animals. Although true, remember that most of the animals we see at our LFS did not swim to the store and arrived at the store the same way that the on-line retailer delivers animals to you in the mail. In fact, it can be argued that purchasing livestock from an on-line vendor is usually easier on the livestock because you are taking one less step ouf of supply chain by skiping the brick and mortar retailer.