Thanks for the advice. Seems everyone is thinking what I was thinking anyway.
I forgot to mention the chain, something else he's expecting the cost of replacement for. I priced everything up off Ebay and came out at £26, so I thought £30 was a fair offer. I've also spoken to 'Agent Ebay', they are pretty non-committal, the expected 'try and resolve it out of Ebay'. Apparently though, if he raises 'an item not as described' case, the worst case scenario is that he has to return it at his own cost for a full refund.
Like was said above, basically its blackmail. Its almost easier to take the hit, I'm still in profit even minus a £60 refund but its the principal of being scammed that annoys me.