um, its not something i would ever do, so i would not be able to tell you where to go.
i just have to watch a fish before i buy, ill spend 45mins just watching a fish at the lfs before i buy it. my lfs owner will even bring me a chair to sit and watch before i buy.
I do know that some people who have gone the online rout are not happy with their purchase, and i have herd plenty of horror story's about some online places.
i did however get in a free trial to test a company's shipping process, the fish i got were alive but not well, and did survive. inverts were dead on pick up.
heres a few sites that i would trust more than others.
(this is a trt member)
(which i have mixed views about)
(i was there once, pretty cool facility)
list is not in order of quality, if its hard to read sorry i just had surgery 3 days ago, my brain is a little loopy