I just bought some fish from eBay.
They arrived in a box with polystrene sheet lining to all internal facings of the box, the middle was then filled with shredded newspaper to prevent the fish from moving.
The fish were double bagged and had a blue sustance in the water I can only assume this is an oxygen agent?
I had 5 fish from this seller all arrived safe and well although I had one casualty 24 hours later but I beleive it was the stress of the journey (not the sellers fault).
They were delivered via Royal Mail next day delivery before 12:00.
Overall I think the seller did a great job in postage and packaging I would use him again if he has any more interesting fish to sell.