I think charging for packing is fine, but I draw the line when people charge "their" time for the packing fees, ie: if they earn £10 an hour in their "proper job" they factor in £5 for half an hour packing.
At those levels, it's not so bad, but what if someone earns £50 an hour? Can they charge £25 packing? What about if David Beckham was the seller? Could he charge his hourly rate?
Let's not forget, packing and sending a frame is a pain. Source a box, carry it home from the bike shop, source some bubble wrap, tape, more cardboard for extra protection, lug it to the PO / stay in for a courier, panic for 2 days that it won't arrive ...
For a fixed price sale you can factor all that into the price of the frame and charge postage at cost, but in an auction you can't.