FWIW last week I sold some zoanthid frags back to my lfs and got $140 for them 8). These were a common variety (Z. sociatus?) Sorta like selling dandelions to your local garden store.
How rare is rare...i posted a thread on the rarest corals...now Zoo's definitely didnt come up on that discussion...i really doubt metallic blue zoos are "rare"....Like i said Frags.org...i guarantee you'll find them for much cheaper...
I think the issue here is, plenty of people see things they like and have no problem spening double triple the worth of something if they want that particular piece at that moment. 600$ to me is a huge amount of money, to some others it is chump change.
I say good for the seller and good for the buyer!
I hope the whole transaction goes smoothly.
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Wow, you two better treat the wify nice then. Don't ever let them find out about reef plagues, you might come home to a new mantis coverred in Manajo's eating your fish while the crown-of-thorns munches on your reef!!