Many of their prices are below the wholesale cost that we purchase them for at the LFS I work at. I would agree, this is probably too good to be true.
It could be some sort of transshipping outfit, where they order them direct from the islands, water change them, re-oxgenate the bags and send them to you. Which is a fine way to get live stock for really cheap, but also would be prone to mortality since the fish would be really stressed out. If that's the case I wouldn't order unless you have a quarantine set up.
ltz,
Andy