Blue haddoni carpets do occasionally make their way here from time to time. They're nice too. But what I'm after is gigantea ... they're just a little bit different. I've been told that at one time they were more common than haddoni's, now it's the other way around.
The link Evan showed is a good site that shows the difference.
BonsaiNut on RC has the most incredible looking gigantea I've ever seen. I should dig up the threads and I'll post them maybe, it's just incredible.
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I'll call the guy tomorrow and ask about the stuff mentioned and then report back what I find.
Anne, I don't think I've said it before, so here goes. Welcome to Canreef!
In answer to your question though .. I'm afraid I don't have a good answer. I think you have to rely on the good word of the person selling you the fish, who in turn has to rely on the good word of the person selling him or her the fish, and so on. If you don't know the person you're dealing with .. then there's probably no good method. Ask around to others and find who they recommend dealing with and in time you'll get a good feel.