Bomberman – it wouldn’t be fair if you started haggling with him about the postage cost. That £20 might be the cost to the other person asking the question for the seller jumping in his car and delivering it by hand (potentially).
I’d request an invoice, or paypal him with the £20 postage included as an additional charge or something. Paypal will refund you if it all kicks off so you’ll not lose out.
If you neg, strop, etc. then you’ve lost a bargain Orange amp. Just remember that’s the goal here. You did bid on it knowing the postage was £20, NOT £7 so drop that notion of getting it cheaper.
If he was really switched on he pretend to post the frame, it’ll get ‘lost’ in transit, then he’ll refund you money….