His claim for the "shipping charges" is without merit. Even if the bike was completely different from the description, it would still not automatically entitle the buyer for the refund of his shipping expenses. Some businesses do it, some don't. It is a matter of checking the "terms and conditions" beforehand. For one example, if you get sent a completely wrong item by a merchant on Amazon, Amazon will resolve the dispute, but the shipping charges (both ways!) will still be on you.
Truing the wheel is indeed normal maintenance, especially on a 8-year old bike.
Your offer to pay for the spoke is perfectly fair, reasonable and sufficient.