I guess you're planning on staying in Kata? It doesn't really matter whether the dive shop is located there or in some other place on Phuket. The reason I say this is that there are only a limited number of day boats and many times that number of dive shops. Nearly all dive shops and agents use pretty much the same boats, so you can get whatever you need from any of us. To take the example of the two shops mentioned already in this thread, PSC (while a very fine operator) doesn't have its own dayboat, so if you book through them or through me or through any number of other shops/agents, they can book you onto a variety of boats, including the SeaBees boat, depending on your personal needs. If you book through SeaBees, who do have their own boat, they will basically offer you just their own itineraries, so the choice is more limited. In other words, any of us anywhere on the island can help you sort out your dives, even if we're located somewhere other than Kata.