I have had very good experiences ordering online from almost every source I have tried. The "safest" IMO is live aquaria. The customer service is the best I have seen, not only for fish, but any customer service I have ever used in general.
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IMO there is really only 1 type of butterfly fish that is a zooplankton feeder that will not touch the reef critters and that is yellow pyramid butterfly fish. I have 3 in my 120 and love them. They have not been aggressive with each other or any other fish. They sometimes stare each other down and aim their spiny top fins at defensive measures, but nothing aggressive.
Many of the other species are hit and miss seemingly on an individual fish basis.
Petco online = Quality Marine = same wholesaler Liveaquaria uses. The difference is they don't seem to pack as well (maybe LA pays extra for better shipping?), and God help you if you ever have to deal with Petco's customer service.